serial: max310x: Fix sparse warnings

sparse warnings: (new ones prefixed by >>)

>> drivers/tty/serial/max310x.c:906:45: sparse: incorrect type in argument 2 (different address spaces)
 drivers/tty/serial/max310x.c:906:45: expected void const [noderef] <asn:1>*from
 drivers/tty/serial/max310x.c:906:45: got struct serial_rs485 *<noident>
>> drivers/tty/serial/max310x.c:938:35: sparse: incorrect type in argument 1 (different address spaces)
 drivers/tty/serial/max310x.c:938:35: expected void [noderef] <asn:1>*to
 drivers/tty/serial/max310x.c:938:35: got struct serial_rs485 *<noident>

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>