ARM: 8816/1: dma-mapping: fix potential uninitialized return

[ Upstream commit c2a3831df6dc164af66d8d86cf356a90c021b86f ]

While trying to use the dma_mmap_*() interface, it was noticed that this
interface returns strange values when passed an incorrect length.

If neither of the if() statements fire then the return value is
uninitialized. In the worst case it returns 0 which means the caller
will think the function succeeded.

Fixes: 1655cf88 ("ARM: dma-mapping: Remove traces of NOMMU code")
Signed-off-by: Nathan Jones <nathanj439@gmail.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>