staging: rtl8723bs: fix code style comparison warning

checkpatch gives the following WARNING:
WARNING: Comparisons should place the constant on the right side of the test
this patch fixes the coding style warning.
Signed-off-by: Kurt Manucredo <fuzzybritches@protonmail.com>
Link: https://lore.kernel.org/r/20210219182331.8-1-fuzzybritches@protonmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/core/rtw_wlan_util.c

@@ -2146,7 +2146,7 @@ void rtw_get_sec_iv(struct adapter *padapter, u8 *pcur_dot11txpn, u8 *StaAddr)
 	struct security_priv *psecpriv = &padapter->securitypriv;
 
 	memset(pcur_dot11txpn, 0, 8);
-	if (NULL == StaAddr)
+	if (!StaAddr)
 		return;
 	psta = rtw_get_stainfo(&padapter->stapriv, StaAddr);
 	DBG_871X("%s(): StaAddr: %02x %02x %02x %02x %02x %02x\n",