Fix movw on x86/x86_64 to accept any 16bits immediate.

Change-Id: I282eece0cd497431f207cec61852b4585ed3655c
diff --git a/compiler/utils/x86/assembler_x86.cc b/compiler/utils/x86/assembler_x86.cc
index a2cbd8b..4c7c4e9 100644
--- a/compiler/utils/x86/assembler_x86.cc
+++ b/compiler/utils/x86/assembler_x86.cc
@@ -248,7 +248,7 @@
   EmitOperandSizeOverride();
   EmitUint8(0xC7);
   EmitOperand(0, dst);
-  CHECK(imm.is_int16());
+  CHECK(imm.is_uint16() || imm.is_int16());
   EmitUint8(imm.value() & 0xFF);
   EmitUint8(imm.value() >> 8);
 }