xfs: Clear W=1 warning in xfs_iwalk_run_callbacks()

For CONFIG_XFS_DEBUG unset, xfs_iwalk_run_callbacks() generates the
following warning for when building with W=1:

fs/xfs/xfs_iwalk.c: In function ‘xfs_iwalk_run_callbacks’:
fs/xfs/xfs_iwalk.c:354:42: error: variable ‘irec’ set but not used [-Werror=unused-but-set-variable]
  354 |         struct xfs_inobt_rec_incore     *irec;
      |                                          ^~~~
cc1: all warnings being treated as errors

Drop @irec, as it is only an intermediate variable.
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/xfs_iwalk.c

@@ -351,7 +351,6 @@ xfs_iwalk_run_callbacks(
 	int				*has_more)
 {
 	struct xfs_mount		*mp = iwag->mp;
-	struct xfs_inobt_rec_incore	*irec;
 	xfs_agino_t			next_agino;
 	int				error;
 
@@ -361,8 +360,8 @@ xfs_iwalk_run_callbacks(
 
 	/* Delete cursor but remember the last record we cached... */
 	xfs_iwalk_del_inobt(iwag->tp, curpp, agi_bpp, 0);
-	irec = &iwag->recs[iwag->nr_recs - 1];
-	ASSERT(next_agino >= irec->ir_startino + XFS_INODES_PER_CHUNK);
+	ASSERT(next_agino >= iwag->recs[iwag->nr_recs - 1].ir_startino +
+			XFS_INODES_PER_CHUNK);
 
 	if (iwag->drop_trans) {
 		xfs_trans_cancel(iwag->tp);