staging: brcm80211: added firmware validation

Fix for https://bugzilla.kernel.org/show_bug.cgi?id=21872



New function wl_check_firmwares() checks validity of all firmware images
loaded from user space.

Signed-off-by: Roland Vossen <rvossen@broadcom.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>