mtd: devices: mchp48l640: Fix memory leak on cmd

The allocation for cmd is not being kfree'd on the return leading to
a memory leak. Fix this by kfree'ing it.

Addresses-Coverity: ("Resource leak")
Fixes: 88d125026753 ("mtd: devices: add support for microchip 48l640 EERAM")
Signed-off-by: Colin Ian King <[e-mail]>
Reviewed-by: Heiko Schocher <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

drivers/mtd/devices/mchp48l640.c

···
 	if (!ret)
 		*retlen += len;
 
+	kfree(cmd);
 	return ret;
 
 fail: