Fix a few -Wignored-qualifiers warnings.

Review URL: https://codereview.chromium.org/1542143003

Cr-Commit-Position: refs/heads/master@{#33122}

src/compiler/code-generator.h

@@ -53,7 +53,7 @@ class CodeGenerator final : public GapResolver::Assembler {
 
   InstructionSequence* code() const { return code_; }
   FrameAccessState* frame_access_state() const { return frame_access_state_; }
-  Frame* const frame() const { return frame_access_state_->frame(); }
+  Frame* frame() const { return frame_access_state_->frame(); }
   Isolate* isolate() const { return info_->isolate(); }
   Linkage* linkage() const { return linkage_; }
 

src/compiler/frame.h

@@ -228,7 +228,7 @@ class FrameAccessState : public ZoneObject {
     SetFrameAccessToDefault();
   }
 
-  Frame* const frame() const { return frame_; }
+  Frame* frame() const { return frame_; }
 
   int sp_delta() const { return sp_delta_; }
   void ClearSPDelta() { sp_delta_ = 0; }