Eliminate a potential warning about extra format arguments.

runtime/vm/disassembler_x64.cc

Index: runtime/vm/disassembler_x64.cc
diff --git a/runtime/vm/disassembler_x64.cc b/runtime/vm/disassembler_x64.cc
index 3460347b6d73bf310feba1ba74347ca3c78c6238..74646739b24b480efd6d7e5d5b0bf5e590d026bc 100644
--- a/runtime/vm/disassembler_x64.cc
+++ b/runtime/vm/disassembler_x64.cc
@@ -1558,9 +1558,11 @@ int DisassemblerX64::InstructionDecode(uword pc) {
           default:
             mnem = "???";
         }
-        AppendToBuffer(((regop <= 1) ? "%s%c " : "%s "),
-                       mnem,
-                       operand_size_code());
+        if (regop <= 1) {
+          AppendToBuffer("%s%c ", mnem, operand_size_code());
+        } else {
+          AppendToBuffer("%s ", mnem);
+        }
         data += PrintRightOperand(data);
       }
         break;