MAINTAINERS: Remove JZ4780 DMA driver entry

The entry for MIPS Ingenic JZ4780 DMA driver is not up to date anymore.
Zubair Lutfullah Kakakhel's email bounces and no maintenance is
provided.

Suggested-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>