X64: Fix compiler complaint

Review URL: http://codereview.chromium.org/159079

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2514 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/disasm-x64.cc

@@ -1349,7 +1349,7 @@ int DisassemblerX64::InstructionDecode(v8::internal::Vector<char> out_buffer,
         break;
 
       case 0xA9: {
-        int64_t value;
+        int64_t value = 0;
         switch (operand_size()) {
           case WORD_SIZE:
             value = *reinterpret_cast<uint16_t*>(data + 1);