orangefs: fix a oob in orangefs_debug_write

I got a syzbot report: slab-out-of-bounds Read in
orangefs_debug_write... several people suggested fixes,
I tested Al Viro's suggestion and made this patch.

Signed-off-by: Mike Marshall <hubcap@omnibond.com>
Reported-by: syzbot+fc519d7875f2d9186c1f@syzkaller.appspotmail.com

Author: hubcapsc

fs/orangefs/orangefs-debugfs.c

@@ -393,9 +393,9 @@ static ssize_t orangefs_debug_write(struct file *file,
 	 * Thwart users who try to jamb a ridiculous number
 	 * of bytes into the debug file...
 	 */
-	if (count > ORANGEFS_MAX_DEBUG_STRING_LEN + 1) {
+	if (count > ORANGEFS_MAX_DEBUG_STRING_LEN) {
 		silly = count;
-		count = ORANGEFS_MAX_DEBUG_STRING_LEN + 1;
+		count = ORANGEFS_MAX_DEBUG_STRING_LEN;
 	}
 
 	buf = kzalloc(ORANGEFS_MAX_DEBUG_STRING_LEN, GFP_KERNEL);