brcmfmac: switch to C function (__brcmf_err) for printing errors

This will allow extending code and using more detailed messages e.g.
with the help of dev_err.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>