brcmsmac: handle non PCI devices in the phy code

Some code in write_{radio,radio}_reg() should just be run if this is a
pci based device. Add the condition again which was removed in commit:
commit 821e4e93
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>