greybus: arche-platform: svc_reset_gpio can't be invalid in arche_platform_cleanup()

svc_reset_gpio is guaranteed to be valid in arche_platform_cleanup. Drop
the useless check.

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>