f2fs: submit bio after shutdown

Sometimes, some merged IOs could get a chance to be submitted, resulting in
system hang in shutdown test. This issues IOs all the time after shutdown.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -531,6 +531,8 @@ skip:
 	if (fio->in_list)
 		goto next;
 out:
+	if (is_sbi_flag_set(sbi, SBI_IS_SHUTDOWN))
+		__submit_merged_bio(io);
 	up_write(&io->io_rwsem);
 }