drm/i915: Unify modeset and flip paths of intel_crtc_set_config()

Call intel_set_mode() uncondionally from intel_crtc_set_config(), since
the former function is now properly wired to ignore all the modesets if
the mode_changed and active_changed flags are false in crtc_state.

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