brcmsmac: fix read in write_phy_reg

This reverts a unintended change mad in commit.
commit 4b006b11
Author: Arend van Spriel <arend@broadcom.com>
Date:   Thu Dec 8 15:06:54 2011 -0800

    brcm80211: smac: use bcma functions for register access in phy code

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