fbdev: smscufx: Fix several use-after-free bugs

Several types of UAFs can occur when physically removing a USB device.

Adds ufx_ops_destroy() function to .fb_destroy of fb_ops, and
in this function, there is kref_put() that finally calls ufx_free().

This fix prevents multiple UAFs.

Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Link: https://lore.kernel.org/linux-fbdev/20221011153436.GA4446@ubuntu/
Cc: <stable@vger.kernel.org>
Signed-off-by: Helge Deller <deller@gmx.de>