PM: runtime: Return -EINPROGRESS from rpm_resume() in the RPM_NOWAIT case

The prospective callers of rpm_resume() passing RPM_NOWAIT to it may
be confused when it returns 0 without actually resuming the device
which may happen if the device is suspending at the given time and it
will only resume when the suspend in progress has completed.  To avoid
that confusion, return -EINPROGRESS from rpm_resume() in that case.

Since none of the current callers passing RPM_NOWAIT to rpm_resume()
check its return value, this change has no functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>