rtc: mxc_v2: Fix _iomem pointer notation

Fix the iomem pointer notation in order to fix the following sparse
warnings:

drivers/rtc/rtc-mxc_v2.c:280:18: warning: incorrect type in argument 1 (different address spaces)
drivers/rtc/rtc-mxc_v2.c:280:18:    expected void const volatile [noderef] <asn:2>*addr
drivers/rtc/rtc-mxc_v2.c:280:18:    got void *[noderef] <asn:2>ioaddr
drivers/rtc/rtc-mxc_v2.c:329:44: warning: incorrect type in argument 1 (different address spaces)
drivers/rtc/rtc-mxc_v2.c:329:44:    expected void *[noderef] <asn:2>ioaddr
drivers/rtc/rtc-mxc_v2.c:329:44:    got void [noderef] <asn:2>*
drivers/rtc/rtc-mxc_v2.c:339:44: warning: incorrect type in argument 1 (different address spaces)
drivers/rtc/rtc-mxc_v2.c:339:44:    expected void *[noderef] <asn:2>ioaddr
drivers/rtc/rtc-mxc_v2.c:339:44:    got void [noderef] <asn:2>*

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>