x86/emul: Adjust X86EMUL_OPC_EXT_MASK to placate MISRA

Resolves 4740 MISRA R7.2 violations (of 4935, so 96% of them).

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/x86/x86_emulate/x86_emulate.h

@@ -620,7 +620,7 @@ struct x86_emulate_ctxt
  * below).
  * Hence no separate #define-s get added.
  */
-#define X86EMUL_OPC_EXT_MASK         0xffff0000
+#define X86EMUL_OPC_EXT_MASK         0xffff0000U
 #define X86EMUL_OPC(ext, byte)       ((uint8_t)(byte) | \
                                       MASK_INSR((ext), X86EMUL_OPC_EXT_MASK))
 /*