staging: iio: adis16220_core.c: add module.h

This is needed and makes the linux-next merge easier.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>