Fixes below compilation warning.

drivers/tty/serial/omap-serial.c: In function 'serial_omap_irq':
drivers/tty/serial/omap-serial.c:228:29: warning: 'ch' may be used uninitialized in this function [-Wuninitialized]

Fix below sparse warning.

drivers/tty/serial/omap-serial.c:392:52: warning: incorrect type in argument 2 (different signedness)
drivers/tty/serial/omap-serial.c:392:52:    expected int *status
drivers/tty/serial/omap-serial.c:392:52:    got unsigned int *<noident>
Reported-by: NKevin Hilman <khilman@ti.com>
Signed-off-by: NGovindraj.R <govindraj.raja@ti.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de> (for drivers/tty changes)
Signed-off-by: NKevin Hilman <khilman@ti.com>