staging: brcm80211: cleanup si_doattach function for fullmac

si_doattach for the fullmac driver is selected using BCMSDIO
flag. Within the function there are #ifdef BRCM_FULLMAC but
this is implicitly true so these have been removed and the
function itself is now between #ifdef BRCM_FULLMAC instead of
BCMSDIO.

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