[common] Do not implicitly map fallback charging mode to ask on D-Bus

Underneath the hood fallback charging mode and ask mode are equivalent.
However ask mode must not be exposed on D-Bus until device has been
unlocked i.e. blindly mapping fallback charging to produce ask mode
activation is not correct.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

src/usb_moded-common.c

@@ -141,7 +141,7 @@ static const modemapping_t common_modemapping[] =
     {
         .internal_mode = MODE_CHARGING_FALLBACK,
         .hardware_mode = MODE_CHARGING,
-        .external_mode = MODE_ASK,
+        .external_mode = 0,
     },
     {
         .internal_mode = MODE_CHARGER,