Fix X86Assembler::repe_cmpsb

We were emitting the wrong instruction.

This code seems unused in the compiler.

Test: m test-art-host-gtest
Change-Id: I6d990dd76f8a8a081158f2b5936e734db88fa345
diff --git a/compiler/utils/x86/assembler_x86.cc b/compiler/utils/x86/assembler_x86.cc
index 55f7691..3280d0b 100644
--- a/compiler/utils/x86/assembler_x86.cc
+++ b/compiler/utils/x86/assembler_x86.cc
@@ -3587,7 +3587,7 @@
 
 void X86Assembler::repe_cmpsb() {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
-  EmitUint8(0xF2);
+  EmitUint8(0xF3);
   EmitUint8(0xA6);
 }