audio_core: Resolve sign conversion warnings

While were at it, we can also enable sign conversion warnings and other
common warnings as errors to prevent these from creeping back into the
codebase.

src/audio_core/effect_context.cpp

@@ -184,19 +184,19 @@ void EffectAuxInfo::UpdateForCommandGeneration() {
     }
 }
 
-const VAddr EffectAuxInfo::GetSendInfo() const {
+VAddr EffectAuxInfo::GetSendInfo() const {
     return send_info;
 }
 
-const VAddr EffectAuxInfo::GetSendBuffer() const {
+VAddr EffectAuxInfo::GetSendBuffer() const {
     return send_buffer;
 }
 
-const VAddr EffectAuxInfo::GetRecvInfo() const {
+VAddr EffectAuxInfo::GetRecvInfo() const {
     return recv_info;
 }
 
-const VAddr EffectAuxInfo::GetRecvBuffer() const {
+VAddr EffectAuxInfo::GetRecvBuffer() const {
     return recv_buffer;
 }