b43: N-PHY: fix one bit off in parsing RF Ctrl Override arguments

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/b43/phy_n.c b/drivers/net/wireless/b43/phy_n.c
index a45a1f3c..061b01b 100644
--- a/drivers/net/wireless/b43/phy_n.c
+++ b/drivers/net/wireless/b43/phy_n.c
@@ -1031,7 +1031,7 @@
 	u8 index = fls(field);
 	u8 addr, en_addr, val_addr;
 	/* we expect only one bit set */
-	B43_WARN_ON(field & (~(1 << index)));
+	B43_WARN_ON(field & (~(1 << (index - 1))));
 
 	if (dev->phy.rev >= 3) {
 		const struct nphy_rf_control_override_rev3 *rf_ctrl;