We currently set it and hold it when converting from short to leaf
form, then release it only to immediately look it back up again
to do the leaf insert.

Do a bit of refactoring to xfs_attr_leaf_try_add() to avoid this
messy handling of the newly allocated leaf buffer.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Allison Henderson<allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>