replace a wrong fixme in dlls/winmm/playsound.c

[Rémi Assailly]

I tested a software ( a monopoly game ) and the error was that a sound 
was still playing so I think that is not a wine bug.
Before submitting this patch to wine-patches I would like to know what 
do you think about it, what should be WARN, FIXME, if choosing ERR to 
all is correct or if some cases are useless.