iio: Add a helper to free a list of IIO device attributes

We have the same code to free a IIO device attribute list in multiple place.
This patch adds a new helper function to take care of this and replaces the
custom instances with a call to the helper function. Note that we do not need to
call list_del() for each of the list items since we will never look at any of
the list items nor the list itself again.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --cc drivers/iio/iio_core.h
Simple merge

diff --cc drivers/iio/industrialio-buffer.c
Simple merge

diff --cc drivers/iio/industrialio-core.c
Simple merge

diff --cc drivers/iio/industrialio-event.c
Simple merge