leds: lp55xx: fix null deref on firmware load failure

I've stumbled upon a kernel crash and the logs
pointed me towards the lp5562 driver:

> <4>[306013.841294] lp5562 0-0030: Direct firmware load for lp5562 failed with error -2
> <4>[306013.894990] lp5562 0-0030: Falling back to user helper
> ...
> <3>[306073.924886] lp5562 0-0030: firmware request failed
> <1>[306073.939456] Unable to handle kernel NULL pointer dereference at virtual address 00000000
> <4>[306074.251011] PC is at _raw_spin_lock+0x1c/0x58
> <4>[306074.255539] LR is at release_firmware+0x6c/0x138
> ...

After taking a look I noticed firmware_release()
could be called with either NULL or a dangling
pointer.

Fixes: 10c06d17 ("leds-lp55xx: support firmware interface")
Signed-off-by: Michal Kazior <michal@plume.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

drivers/leds/leds-lp55xx-common.c

@@ -201,7 +201,7 @@ static void lp55xx_firmware_loaded(const struct firmware *fw, void *context)
 
 	if (!fw) {
 		dev_err(dev, "firmware request failed\n");
-		goto out;
+		return;
 	}
 
 	/* handling firmware data is chip dependent */
@@ -214,9 +214,9 @@ static void lp55xx_firmware_loaded(const struct firmware *fw, void *context)
 
 	mutex_unlock(&chip->lock);
 
-out:
 	/* firmware should be released for other channel use */
 	release_firmware(chip->fw);
+	chip->fw = NULL;
 }
 
 static int lp55xx_request_firmware(struct lp55xx_chip *chip)