ieee802154: remove unused variable 'val'

Variable 'val' is not being initialized and is later being logically
or'd with DAR_PHY_CTRL4_PROMISCUOUS. Considering this variable is never
being read anyway we may as well remove val altogether.

Cleans up error detected by cppcheck:
drivers/net/ieee802154/mcr20a.c:732: (error) Uninitialized variable: val

Fixes: 8c6ad9cc51 ("ieee802154: Add NXP MCR20A IEEE 802.15.4 transceiver driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>

drivers/net/ieee802154/mcr20a.c

@@ -723,13 +723,11 @@ mcr20a_set_promiscuous_mode(struct ieee802154_hw *hw, const bool on)
 	struct mcr20a_local *lp = hw->priv;
 	int ret;
 	u8 rx_frame_filter_reg = 0x0;
-	u8 val;
 
 	dev_dbg(printdev(lp), "%s(%d)\n", __func__, on);
 
 	if (on) {
 		/* All frame types accepted*/
-		val |= DAR_PHY_CTRL4_PROMISCUOUS;
 		rx_frame_filter_reg &= ~(IAR_RX_FRAME_FLT_FRM_VER);
 		rx_frame_filter_reg |= (IAR_RX_FRAME_FLT_ACK_FT |
 				  IAR_RX_FRAME_FLT_NS_FT);