md-multipath: Use seq_putc() in multipath_status()

A single character (closing square bracket) should be put into a sequence.
Thus use the corresponding function "seq_putc".

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Shaohua Li <sh.li@alibaba-inc.com>

drivers/md/md-multipath.c

@@ -157,7 +157,7 @@ static void multipath_status(struct seq_file *seq, struct mddev *mddev)
 		seq_printf (seq, "%s", rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
 	}
 	rcu_read_unlock();
-	seq_printf (seq, "]");
+	seq_putc(seq, ']');
 }
 
 static int multipath_congested(struct mddev *mddev, int bits)