PM / core: Fix bug in the error handling of async suspend

If async_suspend is enabled for parent and child devices, then
PM framework has to ensure that parent's async suspend gets called
only after child's async suspend is done. In case if child's async
suspend fails with error, then parent's async suspend must not be
invoked. The current code uses async_error to ensure this but there
is a problem with it in __device_suspend(). This function notifies
the completion of child's async suspend before updating its error
via async_error variable. As a result, parent's async suspend gets
invoked even though it's child suspend has failed. Fix this bug by
updating the async_error before notifying the child's completion.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
[ rjw: Rearranged wthitespace ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>