swupdate: fix web-app install from last commit

Signed-off-by: Stefano Babic <sbabic@denx.de>

recipes-support/swupdate/swupdate.inc

@@ -114,7 +114,7 @@ do_install () {
   install -m 0755 swupdate ${D}${bindir}/
 
   install -m 0755 -d ${D}/www
-  if [ x${SWUPDATE_WWW} == "xwebapp" ];then
+  if [ -d ${S}/web-app ];then
 	cp -R --no-dereference --preserve=mode,links -v ${S}examples/www/v2/* ${D}/www
   else
 	install -m 0755 ${S}www/* ${D}/www