md: Fix typo in drivers/md

Correct spelling typo in drivers/md.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 9ab768a..7511ce3 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4124,7 +4124,7 @@
 __ATTR(component_size, S_IRUGO|S_IWUSR, size_show, size_store);
 
 
-/* Metdata version.
+/* Metadata version.
  * This is one of
  *   'none' for arrays with no metadata (good luck...)
  *   'external' for arrays with externally managed metadata,