const_structs.checkpatch: remove drm_connector from the list

In some cases drm_connector_funcs cannot be const. For example,
if the connector is created in one module, and it's passed to
another module and is allowed to be changed by that module as
that module has specific info required to implement it.

CRs-Fixed: 2140653
Change-Id: I9c8c39c1e4a315f5b66aba975f9c93172a05fffe
Signed-off-by: Ray Zhang <rayz@codeaurora.org>