drivers: net: wireless: b43: Fix possible NULL ptr dereference

On the ternary expression the 'e' variable could be NULL dereferenced,
when b43_nphy_get_rf_ctl_over_rev7 function returns NULL.
Signed-off-by: Felipe Pena <felipensp@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43/phy_n.c

@@ -164,6 +164,7 @@ static void b43_nphy_rf_ctl_override_rev7(struct b43_wldev *dev, u16 field,
 		}
 		en_addr = en_addrs[override][i];
 
+		if (e)
 			val_addr = (i == 0) ? e->val_addr_core0 : e->val_addr_core1;
 
 		if (off) {