ext4: reflect error codes from ext4_multi_mount_protect() to its callers

[ Upstream commit 3b50d501 ]

This will allow more fine-grained errno codes to be returned by the
mount system call.

Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Stable-dep-of: a44be64b ("ext4: don't clear SB_RDONLY when remounting r/w until quota is re-enabled")
Signed-off-by: Sasha Levin <sashal@kernel.org>