greybus: firmware: abort if AP_READY fails

Abort if the AP_READY request fails.

Also update the comment suggesting that this operation was a temporary
one.

Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>