Use kernel preferred unsigned int declaration style.

Patch created using:
git ls-files drivers/staging/iio | \
xargs ./scripts/checkpatch.pl -f --fix-inplace --types=unspecified_int

Hand edits restored columns in structure definitions.
Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>