shader: decode upper-half byte stores through shared operand selection

Co-authored-by: fxpw <fxpw@outlook.com>

src/graphics/shader/recompiler/frontend/decode/ShaderDecoder.h

@@ -564,6 +564,7 @@ enum class Opcode {
 	BUFFER_LOAD_DWORDX3,
 	BUFFER_LOAD_DWORDX4,
 	BUFFER_STORE_BYTE,
+	BUFFER_STORE_BYTE_D16_HI,
 	BUFFER_STORE_SHORT,
 	BUFFER_STORE_DWORD,
 	BUFFER_STORE_DWORDX2,