iio: Fixpoint formatted output bugfix

Fix some ADC drivers' _scale interface to correct fixpoint formatted output

Signed-off-by: Roland Stigge <stigge@antcom.de>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Michael Hennerich <Michael.Hennerich@analog.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>