clocksource/drivers/timer-versatile: Clear OF_POPULATED flag

clocksource/drivers/timer-versatile: Clear OF_POPULATED flag

The commit 4f41fe386a94 ("clocksource/drivers/timer-probe: Avoid
creating dead devices") broke the handling of arm,vexpress-sysreg [1].

The arm,vexpress-sysreg device is handled by both timer-versatile.c and
drivers/mfd/vexpress-sysreg.c. While the timer driver doesn't use the
device, the mfd driver still needs a device to probe.

So, this patch clears the OF_POPULATED flag to continue creating the
device.

[1] - https://lore.kernel.org/lkml/20200324175955.GA16972@arm.com/

Fixes: 4f41fe386a94 ("clocksource/drivers/timer-probe: Avoid creating dead devices")
Signed-off-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200324195302.203115-1-saravanak@google.com