staging: brcm80211: remove dma_addrwidth() function

The function dma_addrwidth() always returns the same value so
it is redundant. As such it has been removed.

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>