MAINTAINERS: Change list for ioc_serial to linux-serial.

IOC3 is also being used on SGI MIPS systems but this particular driver is
only being used on IA64 systems so linux-mips made no sense as a list.  Pat
also thinks linux-serial@vger.kernel.org is the better list.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

MAINTAINERS

@@ -3140,7 +3140,7 @@ F:	drivers/net/ioc3-eth.c
 
 IOC3 SERIAL DRIVER
 M:	Pat Gefre <pfg@sgi.com>
-L:	linux-mips@linux-mips.org
+L:	linux-serial@vger.kernel.org
 S:	Maintained
 F:	drivers/serial/ioc3_serial.c