rom.sh: only make rom tarball if release=y

Signed-off-by: Leah Rowe <info@minifree.org>

include/rom.sh

@@ -113,6 +113,6 @@ add_uboot()
 
 mkcoreboottar()
 {
-	[ "$target" = "$tree" ] && return 0
-	[ "$XBMK_RELEASE" = "y" ] && mkrom_tarball "bin/$target"; return 0
+	[ "$target" = "$tree" ] && return 0; [ "$XBMK_RELEASE" = "y" ] && \
+	    [ "$release" != "n" ] && mkrom_tarball "bin/$target"; return 0
 }