mt76: mt7603: add additional EEPROM chip ID

Some newer MT7628 based routers (notably the TP-Link Archer C50 v4) are
shipped with a chip-id of 0x7600 in the on-flash EEPROM. Add this as a
possible valid ID.

Ref: https://bugs.openwrt.org/index.php?do=details&task_id=2781

Suggested-by: Ron Asimi <ron.asimi@gmail.com>
Signed-off-by: David Bauer <mail@david-bauer.net>
Signed-off-by: Felix Fietkau <nbd@nbd.name>