NFC: Use this-> to appease GCC bug related to template lambda.

GCC is unable to properly implicitly capture 'this' in generic lambdas. This bug is not fixed until 7.1.0:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67274

PiperOrigin-RevId: 286083427
Change-Id: Id52437119a123a0b8f20d7af4b8f7067fdab0e86

third_party/mlir/lib/Dialect/SPIRV/Serialization/Serializer.cpp

@@ -1661,7 +1661,8 @@ LogicalResult Serializer::processOperation(Operation *opInst) {
 
       // Then handle all the ops that directly mirror SPIR-V instructions with
       // auto-generated methods.
-      .Default([&](auto *op) { return dispatchToAutogenSerialization(op); });
+      .Default(
+          [&](Operation *op) { return dispatchToAutogenSerialization(op); });
 }
 
 namespace {