iio: adc: tsc2046: fix memory corruption by preventing array overflow

In the Linux kernel, the following vulnerability has been resolved: iio: adc: tsc2046: fix memory corruption by preventing array overflow On one side we have indio_dev->num_channels includes all physical channels + timestamp channel. On other side we have an array allocated only for physical channels. So, fix memory corruption by ARRAY_SIZE() instead of num_channels variable. Note the first case is a cleanup rather than a fix as the software timestamp channel bit in active_scanmask is never set by the IIO core.