staging: brcm80211: use KBUILD_MODNAME as driver name in registration

The driver name was hardcoded and not same as the kernel module file
being build. Although there may be no strong requirement to this it
may provide increased consistency.

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