busybox: generalize bbappend to support different revisions

Latest update to version 1.29.3 in upstream breaks the compatibility
of our bbappend, to avoid it in future updates, this commit
generalizes the bbappend to apply all the 1.29 series.

Signed-off-by: Arturo Buzarra <arturo.buzarra@digi.com>

meta-digi-dey/recipes-core/busybox/busybox_1.29.%.bbappend

@@ -1,6 +1,6 @@
-# Copyright (C) 2013-2018 Digi International.
+# Copyright (C) 2013-2019 Digi International.
 
-FILESEXTRAPATHS_prepend := "${THISDIR}/${BP}:"
+FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
 
 SRC_URI += "file://standby \
             file://standby-actions \