staging: wlan-ng: replace BUG_ON() into WARN_ON() on hfa384x_usbin_callback

This patch avoids using BUG_ON() from driver,
and return from hfa384x_usbin_callback with WARN_ON()
if skb was NULL or data in skb is different from expected one.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>