ramips: fix BR-6478ACv2 support

ramips: fix BR-6478ACv2 support

The wholesale changes introduced in commit f9b8328 missed this DTS file
because it hadn't been merged yet. This patch brings it in line to match
the other mt7620a devices' DTS files.

Additionally, the Internet LED is now labeled correctly and set to unused
by default, since the WAN interface is not known in every configuration.

Using sysupgrade between images before and after this commit will require
the -F flag.

Tested-by: Rohan Murch <rohan.murch@gmail.com>
Signed-off-by: Daniel Gimpelevich <daniel@gimpelevich.san-francisco.ca.us>
[drop internet led default setting]
Signed-off-by: Mathias Kresin <dev@kresin.me>