This makes drm_get_connector_name() thread safe.

[airlied: fix to build.]

Reference: http://lkml.kernel.org/r/645ee6e22cad47d38a2b35c21c8d5fe3@DC1-MBX-01.ptsecurity.ruSigned-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>