mwifiex: Fix NULL pointer dereference in skb_dequeue()

commit c44c040300d7afd79294710313a4989683e2afb1 upstream.

At couple of places in cleanup path, we are just going through the
skb queue and freeing them without unlinking. This leads to a crash
when other thread tries to do skb_dequeue() and use already freed node.

The problem is freed by unlinking skb before freeing it.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>