uboot-imx

mtd, spi: Check if flash pointer is used

If flash pointer is used free it, before probing a new
flash and storing it in flash.

Signed-off-by: Heiko Schocher <hs@denx.de>
Tested-by: Jagannadh Teki <jteki@openedev.com>
Reviewed-by: Jagannadh Teki <jteki@openedev.com>