apm821xx: mx60: increment compat_version

apm821xx: mx60: increment compat_version

meraki_loadaddr=1000000 may not enough to boot openwrt 25.12+ on mx60,
so directly sysupgrade without changing meraki_loadaddr would result
broken, but the u-boot-env partition used to be marked read-only, so
compat_version had better be incremented to show a notification to
direct users to the wiki to prepare the sysupgrade manually.

Signed-off-by: Edward Chow <equu@openmail.cc>
Link: https://github.com/openwrt/openwrt/pull/21912
Signed-off-by: Robert Marko <robimarko@gmail.com>