drm/arm/mali: make malidp_mw_connector_helper_funcs static

drm/arm/mali: make malidp_mw_connector_helper_funcs static

The malidp_mw_connector_helper_funcs is not referenced by name
outside of the file it is in, so make it static to avoid the
following warning:

drivers/gpu/drm/arm/malidp_mw.c:59:41: warning: symbol 'malidp_mw_connector_helper_funcs' was not declared. Should it be static?

Signed-off-by: Ben Dooks (Codethink) <ben.dooks@codethink.co.uk>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191217115309.2133503-1-ben.dooks@codethink.co.uk