iio: hx711: fix bug in reset functionality

Return value in hx711_reset() should indicate status of dout otherwise the
calling function is reporting an error as false positive

If there are two reads too close to each other, then the second one will
never succeed. This happens especially when using buffered mode with both
channels enabled.

When changing the channel on every trigger event the former 100 ms are not
enough for waiting until the device indicates normal mode.

Wait up to 1 second until the device turns into normal mode.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>