The reference driver polled but mentioned it was possible to sleep
for a computed period to know when it's ready to read. However, polling
with minimal sleeps is quick and works. This also improves responsiveness
from the driver.
Testing: tested on ast2400 on quanta-q71l
Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>