mtd: nand: denali_dt: remove dma-mask DT property

The driver sets appropriate DMA mask.  Delete the "dma-mask" DT
property.  See [1] for negative comments for this binding.

[1] https://lkml.org/lkml/2016/2/8/57



Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>