staging: wilc1000: fix incorrect strncasecmp length

The strncasecmp of buff against the literal string RSSI
is using variable length which is zero. This should be instead
using the variable size instead.  Also remove the redundant
variable length.

Detected by PVS-Studio, warning: V575
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/linux_wlan.c

@@ -1074,7 +1074,7 @@ static int mac_ioctl(struct net_device *ndev, struct ifreq *req, int cmd)
 {
 	u8 *buff = NULL;
 	s8 rssi;
-	u32 size = 0, length = 0;
+	u32 size = 0;
 	struct wilc_vif *vif;
 	s32 ret = 0;
 	struct wilc *wilc;
@@ -1098,7 +1098,7 @@ static int mac_ioctl(struct net_device *ndev, struct ifreq *req, int cmd)
 			if (IS_ERR(buff))
 				return PTR_ERR(buff);
 
-			if (strncasecmp(buff, "RSSI", length) == 0) {
+			if (strncasecmp(buff, "RSSI", size) == 0) {
 				ret = wilc_get_rssi(vif, &rssi);
 				netdev_info(ndev, "RSSI :%d\n", rssi);