can: m_can: m_can_read_fifo: fix memory leak in error branch

In m_can_read_fifo(), if the second call to m_can_fifo_read() fails,
the function jump to the out_fail label and returns without calling
m_can_receive_skb(). This means that the skb previously allocated by
alloc_can_skb() is not freed. In other terms, this is a memory leak.

This patch adds a goto label to destroy the skb if an error occurs.

Issue was found with GCC -fanalyzer, please follow the link below for
details.

Fixes: e3938177 ("can: m_can: Disable IRQs on FIFO bus errors")
Link: https://lore.kernel.org/all/20211107050755.70655-1-mailhol.vincent@wanadoo.fr
Cc: stable@vger.kernel.org
Cc: Matt Kline <matt@bitbashing.io>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -517,7 +517,7 @@ static int m_can_read_fifo(struct net_device *dev, u32 rxfs)
 		err = m_can_fifo_read(cdev, fgi, M_CAN_FIFO_DATA,
 				      cf->data, DIV_ROUND_UP(cf->len, 4));
 		if (err)
-			goto out_fail;
+			goto out_free_skb;
 	}
 
 	/* acknowledge rx fifo 0 */
@@ -532,6 +532,8 @@ static int m_can_read_fifo(struct net_device *dev, u32 rxfs)
 
 	return 0;
 
+out_free_skb:
+	kfree_skb(skb);
 out_fail:
 	netdev_err(dev, "FIFO read returned %d\n", err);
 	return err;