iio hid-sensor-trigger: add Kconfig depends on IIO_BUFFER

Building a kernel with my configuration failed with:
> drivers/built-in.o: In function `hid_sensor_setup_batch_mode': staging/drivers/iio/common/hid-sensors/hid-sensor-trigger.c:104: undefined reference to `iio_buffer_set_attrs'
which is fixed by this patch.

Signed-off-by: Alexander Wuerstlein <arw@arw.name>
Fixes: 138bc796 ("iio: hid-sensor-hub: Implement batch mode")
Signed-off-by: Jonathan Cameron <jic23@kernel.org>