overlays: ghost-amp: Change early-disable sequence

In the event that the ENABLE signal from the codec goes low before
RELAY2 has been enabled, wait until the full 1000ms has elapsed then
enable RELAY2 and jump to amp_on_wait, i.e. as if output had been
fully enabled then disabled, rather than returning to the amp_off
idle state.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>