SPU2: Fix class has a constructor with 1 argument that is not explicit warnings.

Codacy.

pcsx2/SPU2/SndOut_Cubeb.cpp

@@ -53,7 +53,7 @@ private:
 	public:
 		ConvertedSampleReader() = delete;
 
-		ConvertedSampleReader(u64* pWritten)
+		explicit ConvertedSampleReader(u64* pWritten)
 			: written(pWritten)
 		{
 		}

pcsx2/SPU2/SndOut_XAudio2.cpp

@@ -57,7 +57,7 @@ private:
 			return state.SamplesPlayed & (m_BufferSize - 1);
 		}
 
-		BaseStreamingVoice(uint numChannels)
+		explicit BaseStreamingVoice(uint numChannels)
 			: m_nBuffers(2)
 			, m_nChannels(numChannels)
 			, m_BufferSize(SndOutPacketSize * m_nChannels * PacketsPerBuffer)