greybus: arche-apb: Drop unnecessary checks

wake_detect_gpio and resetn_gpio are guaranteed to be valid in
apb_ctrl_cleanup() and irq-handler, no need to check for their validity.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>