UBI: fix typo in a message

When a PEB passes the torture test, UBI prints
"do not mark it a bad", but should print "do not mark it as bad".
This patch corrects the typo.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/io.c b/drivers/mtd/ubi/io.c
index d58ceb1..8c1b1c7 100644
--- a/drivers/mtd/ubi/io.c
+++ b/drivers/mtd/ubi/io.c
@@ -465,7 +465,7 @@
 	}
 
 	err = patt_count;
-	ubi_msg("PEB %d passed torture test, do not mark it a bad", pnum);
+	ubi_msg("PEB %d passed torture test, do not mark it as bad", pnum);
 
 out:
 	mutex_unlock(&ubi->buf_mutex);