mini2440: Make it able to save a runtime environment
Without this modification saving a modified environment ends with:
mini2440:/ saveenv
saving environment
could not open /dev/env0: Read-only file system
Signed-off-by: Juergen Beisert <juergen@kreuzholzen.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>