drm/vc4: plane: Use return variable in atomic_check

The vc4_plane_atomic_check() directly returns the result of the final
function it calls.

Using the already defined ret variable to check its content on error,
and a separate return 0 on success, makes it easier to extend.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240621152055.4180873-13-dave.stevenson@raspberrypi.com


Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>