The current code only clobbers a local variable, so the device is left
with a stale mapping pointer.

Cc: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Acked-by: NHiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>