usb: dwc3: omap: fix "unbalanced disables for smps10_out1" on omap5evm

usb: dwc3: omap: fix "unbalanced disables for smps10_out1" on omap5evm

Usually, the vbus_regulator (smps10 on omap5evm) boots up disabled.

Hence calling regulator_disable() indirectly through dwc3_omap_set_mailbox()
during probe leads to:

[   10.332764] WARNING: CPU: 0 PID: 1628 at drivers/regulator/core.c:2853 _regulator_disable+0x40/0x164
[   10.351919] unbalanced disables for smps10_out1
[   10.361298] Modules linked in: dwc3_omap(+) clk_twl6040 at24 gpio_twl6040 palmas_gpadc palmas_pwrbutton
industrialio snd_soc_omap_mcbsp(+) snd_soc_ti_sdma display_connector ti_tpd12s015 drm leds_gpio
drm_panel_orientation_quirks ip_tables x_tables ipv6 autofs4
[   10.387818] CPU: 0 PID: 1628 Comm: systemd-udevd Not tainted 5.17.0-rc1-letux-lpae+ #8139
[   10.405129] Hardware name: Generic OMAP5 (Flattened Device Tree)
[   10.411455]  unwind_backtrace from show_stack+0x10/0x14
[   10.416970]  show_stack from dump_stack_lvl+0x40/0x4c
[   10.422313]  dump_stack_lvl from __warn+0xb8/0x170
[   10.427377]  __warn from warn_slowpath_fmt+0x70/0x9c
[   10.432595]  warn_slowpath_fmt from _regulator_disable+0x40/0x164
[   10.439037]  _regulator_disable from regulator_disable+0x30/0x64
[   10.445382]  regulator_disable from dwc3_omap_set_mailbox+0x8c/0xf0 [dwc3_omap]
[   10.453116]  dwc3_omap_set_mailbox [dwc3_omap] from dwc3_omap_probe+0x2b8/0x394 [dwc3_omap]
[   10.467021]  dwc3_omap_probe [dwc3_omap] from platform_probe+0x58/0xa8
[   10.481762]  platform_probe from really_probe+0x168/0x2fc
[   10.481782]  really_probe from __driver_probe_device+0xc4/0xd8
[   10.481782]  __driver_probe_device from driver_probe_device+0x24/0xa4
[   10.503762]  driver_probe_device from __driver_attach+0xc4/0xd8
[   10.510018]  __driver_attach from bus_for_each_dev+0x64/0xa0
[   10.516001]  bus_for_each_dev from bus_add_driver+0x148/0x1a4
[   10.524880]  bus_add_driver from driver_register+0xb4/0xf8
[   10.530678]  driver_register from do_one_initcall+0x90/0x1c4
[   10.536661]  do_one_initcall from do_init_module+0x4c/0x200
[   10.536683]  do_init_module from load_module+0x13dc/0x1910
[   10.551159]  load_module from sys_finit_module+0xc8/0xd8
[   10.561319]  sys_finit_module from __sys_trace_return+0x0/0x18
[   10.561336] Exception stack(0xc344bfa8 to 0xc344bff0)
[   10.561341] bfa0:                   b6fb5778 b6fab8d8 00000007 b6ecfbb8 00000000 b6ed0398
[   10.561341] bfc0: b6fb5778 b6fab8d8 855c0500 0000017b 00020000 b6f9a3cc 00000000 b6fb5778
[   10.595500] bfe0: bede18f8 bede18e8 b6ec9aeb b6dda1c2
[   10.601345] ---[ end trace 0000000000000000 ]---

Fix this unnecessary warning by checking if the regulator is enabled.

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Link: https://lore.kernel.org/r/af3b750dc2265d875deaabcf5f80098c9645da45.1646744616.git.hns@goldelico.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>