arm-autonomy:init-ifupdown: Fix interfaces.d sub-dir scan

Add a missing line breake ("\") to do_install_append to effectually
append the "/etc/network/interfaces.d/" line into
"/etc/network/interfaces" file.

Change-Id: I1cf4e134639d1f63ada7d068cc2822d1ac4218ea
Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm-autonomy/recipes-core/init-ifupdown/init-ifupdown_1.0.bbappend

@@ -6,7 +6,7 @@
 do_install_append() {
     # Add scan of interfaces.d to interfaces file
     cp -f ${WORKDIR}/interfaces ${WORKDIR}/interfaces.subdir
-    echo "source-directory ${sysconfdir}/network/interfaces.d/"
+    echo "source-directory ${sysconfdir}/network/interfaces.d/" \
         >> ${WORKDIR}/interfaces.subdir
 
     # Create interfaces.d script in case nobody is adding a script