ASoC: sh: fix fsi build warnings for 64 bit

As this driver can now be compiled for ARM64, we get a new warning
as a result of passing a DMA filter data pointer through an 'int':

sound/soc/sh/fsi.c: In function 'fsi_dma_probe':
sound/soc/sh/fsi.c:1372:24: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
     shdma_chan_filter, (void *)io->dma_id,

We already know that we only need the legacy filter function on
arch/sh, so we can hide the legacy DMA interface function
behind an #ifdef. This has the other advantage of no longer
depending on the shdma_chan_filter function to be visible.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>