drm/tests: hdmi: return meaningful value from set_connector_edid()

The set_connector_edid() function returns a bogus 0, performing the
check on the connector->funcs->fill_modes() result internally. Make the
function pass the fill_modes()'s return value to the caller and move
corresponding checks to the caller site.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241130-hdmi-mode-valid-v5-3-742644ec3b1f@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>