rtlwifi: Fix smatch warning in pci.c

Smatch reports the following:
  CHECK   drivers/net/wireless/rtlwifi/pci.c
drivers/net/wireless/rtlwifi/pci.c:739 _rtl_pci_rx_interrupt() warn: assigning (-98) to unsigned variable 'stats.noise'

The variable 'stats.noise' is not used. That initializer is removed.
Signed-off-by: NLarry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtlwifi/pci.c

@@ -736,7 +736,6 @@ static void _rtl_pci_rx_interrupt(struct ieee80211_hw *hw)
 
 	struct rtl_stats stats = {
 		.signal = 0,
-		.noise = -98,
 		.rate = 0,
 	};
 	int index = rtlpci->rx_ring[rx_queue_idx].idx;