xfs: Add the missed xfs_perag_put() for xfs_ifree_cluster()

xfs_ifree_cluster() calls xfs_perag_get() at the beginning, but forgets to
call xfs_perag_put() in one failed path.
Add the missed function call to fix it.

Fixes: ce92464c

 ("xfs: make xfs_trans_get_buf return an error code")
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>