xfs_mdrestore: Add -i option to built-in help

Currently we are missing -i option from usage().
This patch adds it to this biult-in help.

Signed-off-by: Marco A Benatto <marco.antonio.780@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/mdrestore/xfs_mdrestore.c b/mdrestore/xfs_mdrestore.c
index c49c13a..0bb4ac8 100644
--- a/mdrestore/xfs_mdrestore.c
+++ b/mdrestore/xfs_mdrestore.c
@@ -194,7 +194,7 @@
 static void
 usage(void)
 {
-	fprintf(stderr, "Usage: %s [-V] [-g] source target\n", progname);
+	fprintf(stderr, "Usage: %s [-V] [-g] [-i] source target\n", progname);
 	exit(1);
 }