[MLIR] NFC. Fix unused context warning from Parser.h

[bondhugula]

Summary

NFC. Fix unused context warning from Parser.h.

..include/mlir/Parser/Parser.h:39:38: warning: parameter ‘context’ set but not used [-Wunused-but-set-parameter]
   39 |     Block *parsedBlock, MLIRContext *context, Location sourceFileLoc) {

mlir/include/mlir/Parser/Parser.h

if (ContainerOpT op = dyn_cast<ContainerOpT>(&parsedBlock->front())) {
       op->remove();
       return op;
     }
   }
 
   // If not, then build a new top-level op if a concrete operation type was
   // specified.
   if constexpr (std::is_same_v<ContainerOpT, Operation *>) {
+    (void)context;
     return emitError(sourceFileLoc)
                << "source must contain a single top-level operation, found: "
                << parsedBlock->getOperations().size(),
            nullptr;
   } else {
     static_assert(
         ContainerOpT::template hasTrait<OpTrait::OneRegion>() &&
             (ContainerOpT::template hasTrait<OpTrait::NoTerminator>() ||