iio: adc: tsc2046: add sanity check to avoid to big allocations

To avoid problematic devicetree configurations. Set allocation limit
with error message and suggestion on what can be done to solve this
issue.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20220117082852.3370869-2-o.rempel@pengutronix.de


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>