mwifiex: add NULL checks in driver unload path

If driver load is failed, sometimes few pointers may remain
uninitialized ex. priv->wdev, priv->netdev, adapter->sleep_cfm
This will cause NULL pointer dereferance while unloading the
driver.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kiran Divekar <dkiran@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/mwifiex/init.c b/drivers/net/wireless/mwifiex/init.c
index e05b417..1d0ec57 100644
--- a/drivers/net/wireless/mwifiex/init.c
+++ b/drivers/net/wireless/mwifiex/init.c
@@ -382,7 +382,8 @@
 
 	adapter->if_ops.cleanup_if(adapter);
 
-	dev_kfree_skb_any(adapter->sleep_cfm);
+	if (adapter->sleep_cfm)
+		dev_kfree_skb_any(adapter->sleep_cfm);
 }
 
 /*