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>
diff --git a/drivers/net/wireless/b43/phy_n.c b/drivers/net/wireless/b43/phy_n.c
index 7c970d3..05ee7f1 100644
--- a/drivers/net/wireless/b43/phy_n.c
+++ b/drivers/net/wireless/b43/phy_n.c
@@ -164,7 +164,8 @@
 		}
 		en_addr = en_addrs[override][i];
 
-		val_addr = (i == 0) ? e->val_addr_core0 : e->val_addr_core1;
+		if (e)
+			val_addr = (i == 0) ? e->val_addr_core0 : e->val_addr_core1;
 
 		if (off) {
 			b43_phy_mask(dev, en_addr, ~en_mask);