xfs: fix reservation release commit flag in xfs_bmap_add_attrfork()

xfs_bmap_add_attrfork() passes XFS_TRANS_PERM_LOG_RES to xfs_trans_commit()
to indicate that the commit should release the permanent log reservation
as part of the commit. This is wrong - the correct flag is
XFS_TRANS_RELEASE_LOG_RES - and it is only by the chance that both these
flags have the value of 0x4 that the code is doing the right thing.

Fix it by changing to use the correct flag.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>