brcm80211: fmac: stop referencing brcmf_sdio in common layer

brcmf_sdio is the data structure for sdio bus layer. Stop
referencing brcmf_sdio from common layer. This patch is part of
the fullmac bus interface refactoring.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>