can: mcp251xfd: mcp251xfd_ring_init(): use %d to print free RAM

In case of an erroneous ring configuration more RAM than available
might be used. Change the printf modifier to a signed int to properly
print this erroneous value.

Fixes: 83daa863 ("can: mcp251xfd: ring: update FIFO setup debug info")
Link: https://lore.kernel.org/20220313083640.501791-2-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c

@@ -261,7 +261,7 @@ int mcp251xfd_ring_init(struct mcp251xfd_priv *priv)
 		   priv->tx->obj_num * priv->tx->obj_size);
 
 	netdev_dbg(priv->ndev,
-		   "FIFO setup: free:                             %4u bytes\n",
+		   "FIFO setup: free:                             %4d bytes\n",
 		   MCP251XFD_RAM_SIZE - (base - MCP251XFD_RAM_START));
 
 	ram_used = base - MCP251XFD_RAM_START;