Using a multi uimage stored in nand didn't work. Only one open for the
bb file is allowed. The file type detection after bootm_open_os_uimage
will fail. bootm_open_initrd_uimage and bootm_open_oftree_uimage already
check if they can reuse data->os.
Signed-off-by: Jan Remmet <j.remmet@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>