libertas: fix format warning

drivers/net/wireless/libertas/if_spi.c: In function ‘if_spi_c2h_data’:
drivers/net/wireless/libertas/if_spi.c:733: warning: format ‘%u’ expects type ‘unsigned int’, but argument 4 has type ‘long unsigned int’
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/if_spi.c

@@ -731,7 +731,7 @@ static int if_spi_c2h_data(struct if_spi_card *card)
 		goto out;
 	} else if (len > MRVDRV_ETH_RX_PACKET_BUFFER_SIZE) {
 		lbs_pr_err("%s: error: card has %d bytes of data, but "
-			   "our maximum skb size is %u\n",
+			   "our maximum skb size is %lu\n",
 			   __func__, len, MRVDRV_ETH_RX_PACKET_BUFFER_SIZE);
 		err = -EINVAL;
 		goto out;