Fix return value of patch_all

Makefile

@@ -81,8 +81,8 @@ endef
 
 #applies all patches in $1 to target directory $2
 define patch_all =
-$(foreach p,$(wildcard $1/*),echo "Applying \"$1\" to \"$2\":"; \
-	cat "$p" | patch -d"$2" -p1; echo "done.";)
+$(foreach p,$(wildcard $1/*),echo "Applying \"$1\" to \"$2\":" && \
+	cat "$p" | patch -d"$2" -p1 && echo "done." && ) true
 endef
 
 CASPER_SOURCE_DIR=$(ISO_CONTENT)/casper