drm/tilcdc: add const to of_device_id

struct of_device_id should normally be const.

Signed-off-by: Xiang wangx <wangxiang@cdjrlc.com>
Reviewed-by: Jyri Sarha <jyri.sarha@iki.fi>
Signed-off-by: Jyri Sarha <jyri.sarha@iki.fi>
Link: https://patchwork.freedesktop.org/patch/msgid/20211216095536.58577-1-wangxiang@cdjrlc.com