[media] st_rc: fix build warning

Building for avr32 leads the following build warning:

drivers/media/rc/st_rc.c:270: warning: passing argument 1 of 'IS_ERR' discards qualifiers from pointer target type
drivers/media/rc/st_rc.c:271: warning: passing argument 1 of 'PTR_ERR' discards qualifiers from pointer target type

devm_ioremap_resource() returns void __iomem *, so change 'base' and
'rx_base' definitions accordingly.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>