dmaengine: sh: rz-dmac: Use list_first_entry_or_null()

dmaengine: sh: rz-dmac: Use list_first_entry_or_null()

Use list_first_entry_or_null() instead of open-coding it with a
list_empty() check and list_first_entry(). This simplifies the code.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Tested-by: John Madieu <john.madieu.xa@bp.renesas.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Tested-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Link: https://patch.msgid.link/20260526084710.3491480-4-claudiu.beznea@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>