iio: adc: at91: call input_free_device() on allocated iio_dev

Current implementation of at91_ts_register() calls input_free_deivce()
on st->ts_input, however, the err label can be reached before the
allocated iio_dev is stored to st->ts_input. Thus call
input_free_device() on input instead of st->ts_input.

Fixes: 84882b06 ("iio: adc: at91_adc: Add support for touchscreens without TSMR")
Signed-off-by: Joe Hattori <joe@pf.is.s.u-tokyo.ac.jp>
Link: https://patch.msgid.link/20241207043045.1255409-1-joe@pf.is.s.u-tokyo.ac.jp


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>