drm: renesas: rz-du: mipi_dsi: Fix return path on error

drm: renesas: rz-du: mipi_dsi: Fix return path on error

In case of error, we should unwind correctly.
Switching to using dmam_ instead of dma_ and moving the code earlier
fixes the issue.

Fixes: 6f392f371650 ("drm: renesas: rz-du: Implement MIPI DSI host transfers")
Suggested-by: Pavel Machek <pavel@nabladev.com>
Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://patch.msgid.link/20260501132135.196701-1-chris.brandt@renesas.com
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>