HID: elan: Fix memleak in elan_input_configured

When input_mt_init_slots() fails, input should be freed
to prevent memleak. When input_register_device() fails,
we should call input_mt_destroy_slots() to free memory
allocated by input_mt_init_slots().

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>