iio: sanity check available_scan_masks array

iio: sanity check available_scan_masks array

When IIO goes through the available scan masks in order to select the
best suiting one, it will just accept the first listed subset of channels
which meets the user's requirements. If driver lists a mask which is a
subset of some of the masks previously in the array of
avaliable_scan_masks, then the latter one will never be selected.

Add a warning if driver registers masks which can't be used due to the
available_scan_masks-array ordering.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/e55ef0b26a6d3b323bab24920c131c79a01ba08e.1697452986.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>