HID: i2c-hid: fix memory leak during probe

In case we are returning from i2c_hid_probe() through the 'err' or
'err_mem_free' labels, there is noone freeing the buffers allocated by
i2c_hid_alloc_buffers().

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