gfs2: clear buf_in_tr when ending a transaction in sweep_bh_for_rgrps

In function sweep_bh_for_rgrps, which is a helper for punch_hole,
it uses variable buf_in_tr to keep track of when it needs to commit
pending block frees on a partial delete that overflows the
transaction created for the delete. The problem is that the
variable was initialized at the start of function sweep_bh_for_rgrps
but it was never cleared, even when starting a new transaction.

This patch reinitializes the variable when the transaction is
ended, so the next transaction starts out with it cleared.

Fixes: d552a2b9b3 ("GFS2: Non-recursive delete")
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/bmap.c

@@ -1632,6 +1632,7 @@ out_unlock:
 			brelse(dibh);
 			up_write(&ip->i_rw_mutex);
 			gfs2_trans_end(sdp);
+			buf_in_tr = false;
 		}
 		gfs2_glock_dq_uninit(rd_gh);
 		cond_resched();