memory: ti-emif-pm: Fix cast to iomem pointer

Cast pointer to iomem memory properly to fix sparse warning:

    drivers/memory/ti-emif-pm.c:251:38: warning: incorrect type in argument 1 (different address spaces)
    drivers/memory/ti-emif-pm.c:251:38:    expected void const volatile [noderef] __iomem *addr
    drivers/memory/ti-emif-pm.c:251:38:    got void *

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>