lt9611uxc_connector_get_modes() propagates the return value of
drm_edid_connector_add_modes() but stores the int temporarily in an
unsigned int. Use the correct type.

Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Neil Armstrong <neil.armstrong@linaro.org>
Cc: Robert Foss <rfoss@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/ed97f4f036263cdc4f34330cef91214970f99a77.1709913674.git.jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>