rtlwifi: rtl8192c-common: Fix sparse warning

Sparse reports the following:

  CHECK   drivers/net/wireless/rtlwifi/rtl8192c/dm_common.c
drivers/net/wireless/rtlwifi/rtl8192c/dm_common.c:570:34: warning: dubious: !x & y

There should be a parens around the expression.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtlwifi/rtl8192c/dm_common.c

@@ -567,7 +567,7 @@ static void rtl92c_dm_dig(struct ieee80211_hw *hw)
 
 	if (rtlpriv->dm.dm_initialgain_enable == false)
 		return;
-	if (!rtlpriv->dm.dm_flag & DYNAMIC_FUNC_DIG)
+	if (!(rtlpriv->dm.dm_flag & DYNAMIC_FUNC_DIG))
 		return;
 
 	rtl92c_dm_ctrl_initgain_by_twoport(hw);