iio: adc/accel: Fix up module licenses

The module license checker complains about these two so just fix
it up. They are both GPLv2, both written by me or using code
I extracted while refactoring from the GPLv2 drivers.

Cc: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>