ar71xx: add missing LED migration for Archer C7
When changing the LED names for the Archer C7 to represent the correct
color, a migration for existing UCI entries was not created.
Add a migration to keep existing LED configurations working.
Fixes commit c79c001b593b ("ar71xx: Archer C7 v1 LED names and RFKILL
fixes")
Signed-off-by: David Bauer <[email protected]>