fs: ext4: Fix alignment of cache buffers

We need to align the cache buffer to ARCH_DMA_MINALIGN in order to avoid
access errors like

CACHE: Misaligned operation at range [be0231e0, be0235e0]

seen on the MCIMX7SABRE.

Fixes: d5aee659 ("fs: ext4: cache extent data")
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: NTom Rini <trini@konsulko.com>
Reviewed-by: NStephen Warren <swarren@nvidia.com>
Tested-by: NPeter Robinson <pbrobinson@gmail.com>

fs/ext4/ext4fs.c

@@ -288,7 +288,7 @@ int ext_cache_read(struct ext_block_cache *cache, lbaint_t block, int size)
 	if (cache->buf && cache->block == block && cache->size == size)
 		return 1;
 	ext_cache_fini(cache);
-	cache->buf = malloc(size);
+	cache->buf = memalign(ARCH_DMA_MINALIGN, size);
 	if (!cache->buf)
 		return 0;
 	if (!ext4fs_devread(block, 0, size, cache->buf)) {