brcm80211: fmac: stop referencing brcmf_pub in bus layer

brcmf_pub is the data structure for common layer. Since brcmf_bus
should be the only structure shared by common layer and bus layer,
stop referencing brcmf_pub from bus 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>