Kernel parameter passed from qemu commandline ignored

Commit ec5c9e8b (Use root.fs on qemu as well) would set the bootargs/bootpath
to null string even in case when the /chosen node exist, the /chosen and boot
property were populated during fdt parsing so do not change in case its already
set.

Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>

slof/fs/root.fs

@@ -47,12 +47,12 @@ THEN
     drop
     new-device
     s" chosen" device-name
+    s" " encode-string s" bootargs" property
+    s" " encode-string s" bootpath" property
+    finish-device
 ELSE
-    extend-device
+    drop
 THEN
-s" " encode-string s" bootargs" property
-s" " encode-string s" bootpath" property
-finish-device
 
 \ Create /aliases
 new-device