MIPS64: Tweak constants used in serialization process to reflect real state.

We do not need to step one instruction further since we do not use Jr to J
optimization anymore for mips64.

TEST=
BUG=

Review URL: https://codereview.chromium.org/1041833002

Cr-Commit-Position: refs/heads/master@{#27504}

src/mips64/assembler-mips64.h

@@ -559,14 +559,11 @@ class Assembler : public AssemblerBase {
   static const int kSpecialTargetSize = 0;
 
   // Number of consecutive instructions used to store 32bit/64bit constant.
-  // Before jump-optimizations, this constant was used in
-  // RelocInfo::target_address_address() function to tell serializer address of
-  // the instruction that follows LUI/ORI instruction pair. Now, with new jump
-  // optimization, where jump-through-register instruction that usually
-  // follows LUI/ORI pair is substituted with J/JAL, this constant equals
-  // to 3 instructions (LUI+ORI+J/JAL/JR/JALR).
-  static const int kInstructionsFor32BitConstant = 3;
-  static const int kInstructionsFor64BitConstant = 5;
+  // This constant was used in RelocInfo::target_address_address() function
+  // to tell serializer address of the instruction that follows
+  // LUI/ORI instruction pair.
+  static const int kInstructionsFor32BitConstant = 2;
+  static const int kInstructionsFor64BitConstant = 4;
 
   // Distance between the instruction referring to the address of the call
   // target and the return address.