Fix bootstrap warning: noinst_PROGRAMS was already defined

utils/Makefile.am:27: warning: noinst_PROGRAMS was already defined in
condition TRUE, which includes condition HAVE_LIBFDT ...

utils/Makefile.am should probably be adding to noinst_PROGRAMS rather
than reclaring it.

Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
(cherry picked from commit 817e669)

utils/Makefile.am

@@ -24,7 +24,7 @@ utils_hooks_30_dtb_updates_LDADD = $(top_builddir)/lib/libpbcore.la \
 		$(FDT_LIBS)
 
 if HAVE_LIBFDT
-noinst_PROGRAMS = \
+noinst_PROGRAMS += \
 	utils/hooks/30-dtb-updates
 endif