spkmodemrecv makefile: add -c to install

a bit pedantic. but that's my intention.

for backwards compatibility with older systems.

this flag means: create the directory. on modern
versions on all systems, it's the default behaviour.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/spkmodem_recv/Makefile

@@ -17,7 +17,7 @@ $(PROG): spkmodem-recv.c
 
 install: $(PROG)
 	mkdir -p $(DESTDIR)$(PREFIX)/bin/
-	install $(PROG) $(DESTDIR)$(PREFIX)/bin/
+	install -c $(PROG) $(DESTDIR)$(PREFIX)/bin/
 
 uninstall:
 	rm -f $(DESTDIR)$(PREFIX)/bin/$(PROG)