tonezone: Fix regression in Australian tone patch

Initialize db to 1.0 instead of doing it in a few, but not all, logic contexts.

Reported-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>
Signed-off-by: Shaun Ruffell <sruffell@digium.com>