serial: mrst_max3110: fix casting warning

max->port.membase is (unsigned char __iomem *); thus,
casting (unsigned char __iomem *) is necessary to fix
the following warning. Also, serial_m3110_ops() is staticized.

drivers/tty/serial/mrst_max3110.c:716:17: warning: symbol 'serial_m3110_ops' was not declared. Should it be static?
drivers/tty/serial/mrst_max3110.c:847:27: warning: incorrect type in assignment (different address spaces)
drivers/tty/serial/mrst_max3110.c:847:27:    expected unsigned char [noderef] <asn:2>*membase
drivers/tty/serial/mrst_max3110.c:847:27:    got void *<noident>

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>