mtd: maps: gpio-addr-flash: Fix ioremapped size

commit 6c925b333368cda4e1b0513b07f72316c0e7edd7 upstream.

We should only iomap the area of the chip that is memory mapped.
Otherwise we could be mapping devices beyond the memory space or that
belong to other devices.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Fixes: ebd71e3a ("mtd: maps: gpio-addr-flash: fix warnings and make more portable")
Cc: <stable@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>