drm2: Fix build after r365264

Fix the build after r365264, I forgot to exclude arm in one more place.

Reported by:	rpokala
Approved by:	manu (implicit, build fix)
MFC after:	3 days
X-MFC-With:	365264
Pointy-hat to:	zeising

sys/dev/drm2/drm_os_freebsd.c

@@ -126,7 +126,9 @@ drm_probe_helper(device_t kdev, const drm_pci_id_list_t *idlist)
 			    device_get_nameunit(kdev), id_entry->name);
 			device_set_desc(kdev, id_entry->name);
 		}
+#if !defined(__arm__)
 		DRM_OBSOLETE(kdev);
+#endif
 		return (-BUS_PROBE_GENERIC);
 	}