wl1271: Check result code of commands

Check the result code of all commands, and return an error code if the
firmware reports an error in execution. Previously this error would go
ignored in most cases.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>