Input: ads7846 - release resources on failure for clean exit

Input device must be released(input_free_device) when ads7846_probe_dt
fails. This fixes the same by releasing resources on failure.

Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>