brcm80211: fmac: only return success in brcmf_sdbrcm_bus_init() when true

The function brcmf_sdbrcm_bus_init() always returned success except for
firmware download failure. However, also when enabling SDIO function 2
is failing the function should return failure. This patch fixes that.

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