Some triggers can only be attached to the IIO device that corresponds to
the same physical device. Currently each driver that requires this
implements its own trigger validation function.

Introduce a new helper function called iio_trigger_validate_own_device()
that can be used to do this check. Having a common implementation avoids
code duplication and unnecessary boiler-plate code.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>