ubifs: Silence error output if MS_SILENT is set

This change completes commit
90bea5a3 ("UBIFS: respect MS_SILENT mount flag")
which already implements support for MS_SILENT except for that one
error message which is still being displayed despite MS_SILENT being
set. Suppress that error message as well in case MS_SILENT is set.
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
[rw: massaged commit message]
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/super.c

@@ -2108,8 +2108,9 @@ static struct dentry *ubifs_mount(struct file_system_type *fs_type, int flags,
 	 */
 	ubi = open_ubi(name, UBI_READONLY);
 	if (IS_ERR(ubi)) {
-		pr_err("UBIFS error (pid: %d): cannot open \"%s\", error %d",
-		       current->pid, name, (int)PTR_ERR(ubi));
+		if (!(flags & MS_SILENT))
+			pr_err("UBIFS error (pid: %d): cannot open \"%s\", error %d",
+			       current->pid, name, (int)PTR_ERR(ubi));
 		return ERR_CAST(ubi);
 	}