xfs: xfs_quota_unreserve_blkres can't fail

Unreserving quotas can't fail due to quota limits, and we'll notice a
shut down file system a bit later in all the callers anyway.  Return
void and remove the error checking and propagation in the callers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>