staging: brcm80211: Fix some initialisation failure paths

Initialise wl_info::tasklet early so that it's safe to tasklet_kill()
it in wl_free().

Remove assertions from wl_free() that may not be true in case of
initialisation failure.

Call wl_release_fw() in case of failure after wl_request_fw().
Don't rely on wl_firmware::fw_cnt in wl_release_fw().

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Henry Ptasinski <henryp@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>