brcmfmac: have sdio return -EIO when device communication is not possible

The bus interface functions txctl and rxctl may be used while the device
can not be accessed, eg. upon driver .remove() callback. This patch will
immediately return -EIO when this is the case which speeds up the module
unload.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>