[turbofan] Fix typo

TBR=neis@chromium.org

Bug: v8:7127
Change-Id: Ic7c98f0f03d57fc748badddb921430818ec2f790
Reviewed-on: https://chromium-review.googlesource.com/819351
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50002}

src/compiler/bytecode-graph-builder.h

@@ -235,7 +235,7 @@ class BytecodeGraphBuilder {
   // feedback.
   CallFrequency ComputeCallFrequency(int slot_id) const;
 
-  // Helper function to extract the speulcation mode from the recorded type
+  // Helper function to extract the speculation mode from the recorded type
   // feedback.
   SpeculationMode GetSpeculationMode(int slot_id) const;