arm64: dma-mapping: Fix FORCE_CONTIGUOUS buffer clearing

We need to invalidate the caches *before* clearing the buffer via the
non-cacheable alias, else in the worst case __dma_flush_area() may
write back dirty lines over the top of our nice new zeros.

Change-Id: Ie1641f5e0ec4f725c15b282fcde2204c3c9fda42
Fixes: dd65a941f6ba ("arm64: dma-mapping: clear buffers allocated with FORCE_CONTIGUOUS flag")
Cc: <stable@vger.kernel.org> # 4.18.x-
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: 3238c359acee4ab57f15abb5a82b8ab38a661ee7
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>