iio: aspeed-adc: wait for initial sequence.

iio: aspeed-adc: wait for initial sequence.

commit 737cc2a593782df6846b3cab7e0f64384f58364a upstream.

This patch enables adc engine at initialization time and waits
for the initial sequence completion before enabling adc channels.

Without this code adc channels are not functional and shows
zeros for all connected channels.

Tested on mellanox msn platform.

v1 -> v2:
Pointed by Rick Altherr:
 - Wait init sequence code enabled by bool
from OF match table.

Signed-off-by: Mykola Kostenok <c_mykolak@mellanox.com>
Reviewed-by: Rick Altherr <raltherr@google.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>