ioremap balanced with iounmap for drivers/mtd subsystem

ioremap must be balanced by an iounmap and failing to do so can result
in a memory leak.

Tested (compilation only) with:
- allmodconfig
- Modifying drivers/mtd/maps/Kconfig and drivers/mtd/nand/Kconfig to
make sure that the changed file is compiling without warning

Signed-off-by: Amol Lad <amol@verismonetworks.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

drivers/mtd/nand/edb7312.c

@@ -198,6 +198,9 @@ static void __exit ep7312_cleanup(void)
 	/* Release resources, unregister device */
 	nand_release(ap7312_mtd);
 
+	/* Release io resource */
+	iounmap((void *)this->IO_ADDR_R);
+
 	/* Free the MTD device structure */
 	kfree(ep7312_mtd);
 }