MAINTAINERS: Correct path to moved files

The driver was moved in commit 1838a7b3 ("mtd: rawnand: Move
drivers for Ingenic SoCs to subfolder").

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@vger.kernel.org