staging: brcm80211: remove unnecessary null check

kfree(NULL) is safe, and the rest of the cleanup should be done regardless
to make sure the state is consistent.

Signed-off-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>