staging: r8188eu: limit rtw_dbg_port to path a

Rf registers can be read by rtw_wx_read_rf or via the private ioctl 0x0B.
The latter calls rtw_dbg_port. Limit rf register reads to path a in
rtw_debug_port.
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220212161737.381841-8-martin@kaiser.cxSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/os_dep/ioctl_linux.c

@@ -3621,7 +3621,11 @@ static int rtw_dbg_port(struct net_device *dev,
 		DBG_88E("write_bbreg(0x%x) = 0x%x\n", arg, rtl8188e_PHY_QueryBBReg(padapter, arg, 0xffffffff));
 		break;
 	case 0x74:/* read_rf */
-		DBG_88E("read RF_reg path(0x%02x), offset(0x%x), value(0x%08x)\n", minor_cmd, arg, rtl8188e_PHY_QueryRFReg(padapter, minor_cmd, arg, 0xffffffff));
+		if (minor_cmd != RF_PATH_A) {
+			ret = -EINVAL;
+			break;
+		}
+		DBG_88E("read RF_reg path(0x%02x), offset(0x%x), value(0x%08x)\n", RF_PATH_A, arg, rtl8188e_PHY_QueryRFReg(padapter, RF_PATH_A, arg, 0xffffffff));
 		break;
 	case 0x75:/* write_rf */
 		if (minor_cmd != RF_PATH_A) {