HID: i2c-hid: also call i2c_hid_free_buffers in i2c_hid_remove

In the case where the hid driver in charge of handling the hid part
of the device (hid-generic for instance) fails at probe, neither
i2c_hid_start nor i2c_hid_stop are called.
Thus, the buffers allocated in i2c_hid_probe are never freed.

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