brcmfmac: add possibility to obtain firmware error

The feature module needs to evaluate the actual firmware error return
upon a control command. This adds a flag to struct brcmf_if that the
caller can set. This flag is checked to determine the error code that
needs to be returned.

Fixes: b69c1df4 ("brcmfmac: separate firmware errors from i/o errors")
Reviewed-by: Hante Meuleman <hante.meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>