xl: don't ignore return value from libxl_device_events_handler

That function can return a whole slew of error codes. Translate them
to EXIT_FAILURE.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>

tools/xl/xl_misc.c

@@ -182,7 +182,7 @@ int main_devd(int argc, char **argv)
         }
     }
 
-    libxl_device_events_handler(ctx, 0);
+    ret = libxl_device_events_handler(ctx, 0) ? EXIT_FAILURE : EXIT_SUCCESS;
 
 out:
     return ret;