Staging: iio: Fix up the module build.

Both the max1363 and lis3l02dq modules rely on IIO trigger support in
their ring buffer implementations, which is presently a separate config
option. In the case of IIO_RING_BUFFER=y and IIO_TRIGGER=n, we end up
with the following:

ERROR: "iio_trigger_attach_poll_func" [drivers/staging/iio/adc/max1363.ko] undefined!
ERROR: "iio_trigger_dettach_poll_func" [drivers/staging/iio/adc/max1363.ko] undefined!
ERROR: "iio_trigger_unregister" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_trigger_notify_done" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_trigger_read_name" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_trigger_poll" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_trigger_attach_poll_func" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_trigger_register" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_free_trigger" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_trigger_dettach_poll_func" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
ERROR: "iio_allocate_trigger" [drivers/staging/iio/accel/lis3l02dq.ko] undefined!
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2

This adds an IIO_TRIGGER select for these two drivers conditional on
IIO ring buffer support. Caught with an SH randconfig in -next.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>