Initialize uninitialized class members. (#2899)

Author: maarquitos14

lib/SPIRV/libSPIRV/SPIRVInstruction.h

@@ -4280,7 +4280,9 @@ class SPIRVUntypedPrefetchKHR : public SPIRVInstruction {
     validate();
   }
 
-  SPIRVUntypedPrefetchKHR() : SPIRVInstruction(OC) {
+  SPIRVUntypedPrefetchKHR()
+      : SPIRVInstruction(OC), PtrTy(SPIRVID_INVALID),
+        NumBytes(SPIRVID_INVALID) {
     setHasNoId();
     setHasNoType();
   }