fm10k: use an unsigned int for i in ethtool_get_strings

The value will never be negative, and we use the %u print format. Thus,
use unsigned int for the loop counter. Issue found using cppcheck.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/fm10k/fm10k_ethtool.c

@@ -124,7 +124,7 @@ static void fm10k_get_strings(struct net_device *dev, u32 stringset, u8 *data)
 {
 	struct fm10k_intfc *interface = netdev_priv(dev);
 	char *p = (char *)data;
-	int i;
+	unsigned int i;
 
 	switch (stringset) {
 	case ETH_SS_TEST: