mt7915: downgrade WA firmware to EAP605's v202303

Using WA firmware from EAP605 fixes the issue of UDP floods
killing MCU communication.

Firmware downloaded from:

https://static.tp-link.com/upload/gpl-code/2023/202305/20230515/eap615-wall_gpl_code.tar.gz

Fixes: openwrt/mt76#776

Signed-off-by: rany <ranygh@riseup.net>