rtl_bt: Update RTL8852B BT USB firmware to 0xDBC6_B20F

This firmware patch update for Realtek RTL8852B BT USB controller.

Release Version: 0xDBC6_B20F

Signed-off-by: Hilda Wu <hildawu@realtek.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>