staging: brcm80211: cleaned up prefix for utility functions

Code cleanup. 'bcm' replaced by 'brcmu_', which is shorthand for
'Broadcom Utilities' (the 'brcmutil.ko' library module).

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