drm/i915: Don't look at staged config crtc when changing DRRS state

The function intel_dp_set_drrs_state() would decide which pipe to
downclock based on the staged config for the given connector. However,
the result of that function is immediate, and it uses input values from
crtc->config, so it should be looking at the current crtc instead.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>