ASoC: rt5682: Prefer async probe

The probe of rt5682 is pretty slow.  A quick measurement shows that it
takes ~650 ms on at least one board.  There's no reason to block all
other drivers waiting for this probe to finish.  Set the flag to allow
other drivers to probe while we're probing.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20200828162005.1.I4f67f494c4f759b0e5c7f487e040dfdcf16e0876@changeid


Signed-off-by: Mark Brown <broonie@kernel.org>