Update e8910.c

Fix sound issue on platform (ex: arm 64 like rgb30) where char are unsigned by default

Author: zx81zx81

e8910.c

@@ -35,7 +35,7 @@ struct AY8910 {
 int CountA,CountB,CountC,CountN,CountE;
 int RNG;
 unsigned VolA,VolB,VolC,VolE;
-char CountEnv;
+signed char CountEnv;
 unsigned char EnvelopeA,EnvelopeB,EnvelopeC;
 unsigned char OutputA,OutputB,OutputC,OutputN;
 unsigned char Hold,Alternate,Attack,Holding;