tty: serial: msm_serial: Constify msm_uart_pops

tty: serial: msm_serial: Constify msm_uart_pops

The only usage of msm_uart_pops is to assign its address to the ops
field in the uart_port struct, which is a pointer to const. Make it
const to allow the compiler to put it in read-only memory.

Reviewed-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20201104235134.17793-1-rikard.falkeborn@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>