HID: multitouch: devm conversion

HID special drivers can use safely the devres API.
Use it to remove 25 lines of code and to clean up a little the error paths.

Besides the basic kzalloc -> devm_kzalloc conversions, I changed the
place of the allocation of the new name. Doing this right in
mt_input_configured() removes the kstrdup call which was not very helpful
and the new way is simpler to understand (and to debug).

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>