[CIFS] update limit for snprintf in cifs_construct_tcon

In 34c87901e113 "Shrink stack space usage in cifs_construct_tcon" we
change the size of the username name buffer from MAX_USERNAME_SIZE
(256) to 28.  This call to snprintf() needs to be updated as well.
Reported by Dan Carpenter.

Reviewed-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index dbd669c..ccc1afa 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3485,7 +3485,7 @@
 		goto out;
 	}
 
-	snprintf(username, MAX_USERNAME_SIZE, "krb50x%x", fsuid);
+	snprintf(username, sizeof(username), "krb50x%x", fsuid);
 	vol_info->username = username;
 	vol_info->local_nls = cifs_sb->local_nls;
 	vol_info->linux_uid = fsuid;