include: nand: move endif to end of file

The terminator endif of ifdef _NAND_H_ should be at the
end of file as a fail safe.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>