i2c: amd-mp2: Remove useless DMA-32 fallback configuration

As stated in [1], dma_set_mask() with a 64-bit mask never fails if
dev->dma_mask is non-NULL. So, if it fails, the 32 bits case will also
fail for the same reason.

Simplify code and remove some dead code accordingly.

[1]: https://lkml.org/lkml/2021/6/7/398



Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Nehal Bakulchandra Shah <Nehal-bakulchandra.Shah@amd.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>