Fix the tones playing count in InCallTonePlayer

Current code always reset the number of tones playing
to 0 whenever any tone is stopped. This causes issues
when more than one incall tones are playing at the same time.
For example, if MO call local ringback tone and MT call
waiting tones are played together and ringback tone is
stopped, the call waiting tone keeps playing forever.
Fix the code which decrements the tones count.

Bug: 243878143
Change-Id: I2cdd511938f8bd809e89a84194d66997330992c3