mtd/spi: fix block count for is25lq040b

This spi-nor is 4Mbit/512KB

Fixes: b4fbcbc5a5 ("mtd/spi: add support for is25lq040b")
Signed-off-by: Sean Nyekjaer <sean.nyekjaer@prevas.dk>
Reviewed-by: Jagan Teki <jagan@openedev.com>
1 file changed