serial: don't add msm_serial's probe function to the driver struct

msm_serial_driver is registered using platform_driver_probe which takes
care for the probe function itself.  So don't pass it in the driver
struct, too.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>