[media] rc-main: Re-apply filter for no-op protocol change

Since commit da6e162d6a46 ("[media] rc-core: simplify sysfs code"), when
the IR protocol is set using the sysfs interface to the same set of
protocols that are already set, store_protocols() does not refresh the
scancode filter with the new protocol, even if it has already called the
change_protocol() callback successfully. This results in the filter
being disabled in the hardware and not re-enabled until the filter is
set again using sysfs.

Fix in store_protocols() by still re-applying the filter whenever the
change_protocol() driver callback succeeded.

The problem can be reproduced with the img-ir driver by setting a
filter, and then setting the protocol to the same protocol that is
already set:
$ echo nec > protocols
$ echo 0xffff > filter_mask
$ echo nec > protocols

After this, messages which don't match the filter were still being
received.

Fixes: da6e162d6a46 ("[media] rc-core: simplify sysfs code")

Reported-by: Sifan Naeem <sifan.naeem@imgtec.com>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: David Härdeman <david@hardeman.nu>
Cc: <stable@vger.kernel.org> # v3.17+
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/rc/rc-main.c

@@ -1021,16 +1021,16 @@ static ssize_t store_protocols(struct device *device,
 		goto out;
 	}
 
-	if (new_protocols == old_protocols) {
-		rc = len;
-		goto out;
+	if (new_protocols != old_protocols) {
+		*current_protocols = new_protocols;
+		IR_dprintk(1, "Protocols changed to 0x%llx\n",
+			   (long long)new_protocols);
 	}
 
-	*current_protocols = new_protocols;
-	IR_dprintk(1, "Protocols changed to 0x%llx\n", (long long)new_protocols);
-
 	/*
-	 * If the protocol is changed the filter needs updating.
+	 * If a protocol change was attempted the filter may need updating, even
+	 * if the actual protocol mask hasn't changed (since the driver may have
+	 * cleared the filter).
 	 * Try setting the same filter with the new protocol (if any).
 	 * Fall back to clearing the filter.
 	 */