xen-hvm: Remove redundant variable 'xstate'

In xen_hvm_change_state_handler(), we can pass 'opaque' with type cast
to xen_main_loop_prepare() directly, there's no need to use additional
variable for it.
Signed-off-by: NChen Gang <gang.chen.5i5j@gmail.com>
Acked-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

xen-hvm.c

@@ -993,9 +993,8 @@ static void xen_main_loop_prepare(XenIOState *state)
 static void xen_hvm_change_state_handler(void *opaque, int running,
                                          RunState rstate)
 {
-    XenIOState *xstate = opaque;
     if (running) {
-        xen_main_loop_prepare(xstate);
+        xen_main_loop_prepare((XenIOState *)opaque);
     }
 }