mtd: rawnand: free the nand_device object

This patch releases the resources allocated in nanddev_init function.

Fixes: a7ab085d ("mtd: rawnand: Initialize the nand_device object")
Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1579767768-32295-1-git-send-email-christophe.kerello@st.com