pata_imx: use void __iomem * for regs

regs is returned from ioremap, so add a __iomem. Also, make it
void * instead of u8 *.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>