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>

fs/xfs/xfs_inode.c

@@ -2634,8 +2634,10 @@ xfs_ifree_cluster(
 		error = xfs_trans_get_buf(tp, mp->m_ddev_targp, blkno,
 				mp->m_bsize * igeo->blocks_per_cluster,
 				XBF_UNMAPPED, &bp);
-		if (error)
+		if (error) {
+			xfs_perag_put(pag);
 			return error;
+		}
 
 		/*
 		 * This buffer may not have been correctly initialised as we