dmaengine: sh: rz-dmac: Allow for multiple DMACs

dma_request_channel() calls into __dma_request_channel() with
NULL as value for np, which won't allow for the selection of the
correct DMAC when multiple DMACs are available.

Switch to using __dma_request_channel() directly so that we can
choose the desired DMA for the channel. This is in preparation
of adding DMAC support for the Renesas RZ/V2H(P) and similar SoCs.

Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20250423143422.3747702-5-fabrizio.castro.jz@renesas.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>