dmaengine: imx-sdma: add clock ratio 1:1 check

On i.mx8 mscale B0 chip, AHB/SDMA clock ratio 2:1 can't be supportted,
since SDMA clock ratio has to be increased to 250Mhz, AHB can't reach
to 500Mhz, so use 1:1 instead.

Based on NXP commit MLK-16841-1 by Robin Gong <yibin.gong@nxp.com>

Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Vinod Koul <vkoul@kernel.org>