brcm80211: fmac: rename structure brcmf_bus to brcmf_sdio

Rename sdio bus structure brcmf_bus to brcmf_sdio for preparation
of USB bus support. This patch is part of the fullmac bus interface
refactoring.

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