drm/udl: Add missing static storage class specifiers in udl_connector.c

Fixes the following sparse warnings:
drivers/gpu/drm/udl/udl_connector.c:80:20: warning:
symbol 'udl_best_single_encoder' was not declared. Should it be static?
drivers/gpu/drm/udl/udl_connector.c:93:5: warning:
symbol 'udl_connector_set_property' was not declared. Should it be static?
drivers/gpu/drm/udl/udl_connector.c:106:35: warning:
symbol 'udl_connector_helper_funcs' was not declared. Should it be static?
drivers/gpu/drm/udl/udl_connector.c:112:28: warning:
symbol 'udl_connector_funcs' was not declared. Should it be static?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>