Fix mp3.c compiler warnings
Fix mp3.c compiler warnings

uklauer/sox,jacksonh/sox,cbagwell/sox,jacksonh/sox,MageSlayer/sox,MageSlayer/sox,Motiejus/sox,cbagwell/sox,CaptainHayashi/sox,CaptainHayashi/sox,MageSlayer/sox,uklauer/sox,mhartzel/sox_personal_fork,mhartzel/sox_personal_fork,mhartzel/sox_personal_fork,jacksonh/sox,pcqpcq/sox,Motiejus/sox,MageSlayer/sox,Motiejus/sox,pcqpcq/sox,jacksonh/sox,cbagwell/sox,mhartzel/sox_personal_fork,uklauer/sox,CaptainHayashi/sox,cbagwell/sox,pcqpcq/sox,pcqpcq/sox,uklauer/sox,CaptainHayashi/sox,MageSlayer/sox,Motiejus/sox