layer.conf: Add hardknott to LAYERSERIES_COMPAT

hardknott is codename for 3.3 release

Signed-off-by: Khem Raj <raj.khem@gmail.com>

conf/layer.conf

@@ -9,6 +9,6 @@ BBFILE_COLLECTIONS += "swupdate"
 BBFILE_PATTERN_swupdate := "^${LAYERDIR}/"
 BBFILE_PRIORITY_swupdate = "6"
 
-LAYERSERIES_COMPAT_swupdate = "dunfell gatesgarth"
+LAYERSERIES_COMPAT_swupdate = "dunfell gatesgarth hardknott"
 
 LAYERDEPENDS_swupdate = "openembedded-layer"