mt7622: remove 300 MHz from dts

mt7622: remove 300 MHz from dts

Due to the bug described here[1], remove the 300 MHz clock to avoid a low
voltage condition that can cause a hang when rebooting the RT3200/E8450.

This solution is probably better than the script-based work-around[2].

1. https://forum.openwrt.org/t/belkin-rt3200-linksys-e8450-wifi-ax-discussion/94302/1490
2. https://github.com/openwrt/openwrt/pull/5025

Signed-off-by: John Audia <therealgraysky@proton.me>
Tested-by: Rui Salvaterra <rsalvaterra@gmail.com>
Tested-by: John Audia <therealgraysky@proton.me>