iommu/mediatek: Fix forever loop in error handling

There is a typo so this loop does i++ where i-- was intended.  It will
result in looping until the kernel crashes.

Fixes: 26593928 ("iommu/mediatek: Add error path for loop of mm_dts_parse")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/Y5C3mTam2nkbaz6o@kili


Signed-off-by: Joerg Roedel <jroedel@suse.de>