staging: add module.h to various iio drivers

Since they are assuming it is there implicitly and will fail otherwise
with things like:

drivers/staging/iio/impedance-analyzer/ad5933.c:816: warning: type
 defaults to ‘int’ in declaration of ‘MODULE_AUTHOR’

drivers/staging/iio/adc/ad7280a.c:990: warning: type defaults to ‘int’
 in declaration of ‘MODULE_AUTHOR’

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>