greybus: arche-platform: arche_pdata is guaranteed to be valid

arche_pdata is guaranteed to be valid in arche_platform_remove().

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>