ASoC: fsl_asrc_dma: fix eDMA maxburst misalignment with channel count

ASoC: fsl_asrc_dma: fix eDMA maxburst misalignment with channel count

The back-end consumes data in units of the number of channels. When the
maxburst value is not evenly divisible by the channel count, the DMA
transfer length does not align with the FIFO frame boundary, causing
wrong data to be copied and audible noise at the end of the stream.

This is specific to eDMA: eDMA only responds to DMA requests from the
back-end, whereas SDMA handles requests from both the front-end and the
back-end and is not affected.

For eDMA, when the back-end maxburst is not evenly divisible by the
channel count, align it to the nearest valid boundary:
- If maxburst >= channel count, override to the channel count so each
  transfer corresponds to exactly one audio frame.
- If maxburst < channel count, override to 1 to avoid partial-frame
  transfers.

Retain the original maxburst for SDMA or when it already aligns with
the channel count.

Fixes: c05f10f28ef6 ("ASoC: fsl_asrc: Add support for imx8qm & imx8qxp")
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://patch.msgid.link/20260625102416.424911-1-shengjiu.wang@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>