brcmfmac: use unified dongle address preparation function
Introduce a unified dongle backplane address preparation function
brcmf_sdio_addrprep to replace duplicate address prep code.
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com> Reviewed-by: Arend van Spriel <arend@broadcom.com> Signed-off-by: Franky Lin <frankyl@broadcom.com> Signed-off-by: Arend van Spriel <arend@broadcom.com> Signed-off-by: John W. Linville <linville@tuxdriver.com>