x86/HVM: fix xsm_op for 32-bit guests

Like for PV, 32-bit guests need to invoke the compat handler, not the
native one.

Fixes: db984809d6 ("hvm: wire up domctl and xsm hypercalls")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/hvm/hypercall.c

@@ -138,7 +138,7 @@ static const struct {
     HYPERCALL(event_channel_op),
     COMPAT_CALL(sched_op),
     COMPAT_CALL(set_timer_op),
-    HYPERCALL(xsm_op),
+    COMPAT_CALL(xsm_op),
     HYPERCALL(hvm_op),
     HYPERCALL(sysctl),
     HYPERCALL(domctl),