[mlir][SPIRV] Fix blocks nested too deeply error.

[mravishankar]

Summary

Issue arises due to a giant if/else if/else/... construct. Changing
them to just ifs.

[antiagainst]

Actually less code! :)

mlir/tools/mlir-tblgen/SPIRVUtilsGen.cpp

static void emitSerializationFunction(const Record *attrClass,
   os << "}\n\n";
 }
 
 /// Generates the prologue for the function that dispatches the serialization of
 /// the operation `opVar` based on its opcode.
 static void initDispatchSerializationFn(StringRef opVar, raw_ostream &os) {
   os << formatv(
       "LogicalResult Serializer::dispatchToAutogenSerialization(Operation "
-      "*{0}) {{\n ",
+      "*{0}) {{\n",
       opVar);
 }
 
 /// Generates the body of the dispatch function. This function generates the
 /// check that if satisfied, will call the serialization function generated for
 /// the `op`.
 static void emitSerializationDispatch(const Operator &op, StringRef tabs,
                                       StringRef opVar, raw_ostream &os) {
   os << tabs
      << formatv("if (isa<{0}>({1})) {{\n", op.getQualCppClassName(), opVar);
   os << tabs
      << formatv("  return processOp(cast<{0}>({1}));\n",
                 op.getQualCppClassName(), opVar);
-  os << tabs << "} else";
+  os << tabs << "}\n";
 }
 
 /// Generates the epilogue for the function that dispatches the serialization of
 /// the operation.
 static void finalizeDispatchSerializationFn(StringRef opVar, raw_ostream &os) {
-  os << " {\n";
   os << formatv(
-      "    return {0}->emitError(\"unhandled operation serialization\");\n",
+      "  return {0}->emitError(\"unhandled operation serialization\");\n",
       opVar);
-  os << "  }\n";
-  os << "  return success();\n";
   os << "}\n\n";
 }
 
 /// Generates code to deserialize the attribute of a SPV_Op into `os`. The
 /// generated code reads the `words` of the serialized instruction at
 /// position `wordIndex` and adds the deserialized attribute into `attrList`.
 static void emitAttributeDeserialization(const Attribute &attr,
                                          ArrayRef<SMLoc> loc, StringRef tabs,