linux-firmware: update firmware for mediatek bluetooth chip (MT7921)

Update binary firmware for MT7921 BT devices.

File: mediatek/BT_RAM_CODE_MT7961_1_2_hdr.bin
Version: 20230331111156

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>