Ensure that querying the IIO buffer scan_mask returns a value of
0 or 1. Currently querying the scan mask has the value returned
by test_bit(), which returns either true or false. For some
architectures test_bit() may return -1 for true, which will appear
to return an error when returning from iio_scan_mask_query().

Additionally, it's important for the sysfs interface to consistently
return the same thing when querying the scan_mask.
Signed-off-by: NAlec Berg <alecaberg@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: NJonathan Cameron <jic23@kernel.org>