brcmsmac: fix DMA on SoCs

These extra offsets are only needed by PCIe devices and not when
running on an SoC.

This partly reverts commit:
commit 821e4e93172e4f7d5ac1eade04665c3dc5049c4a
Author: Roland Vossen <rvossen@broadcom.com>
Date:   Mon Aug 8 15:58:58 2011 +0200

    staging: brcm80211: removed unused bus code from softmac

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>