Do not rely on crtc->config any more. Remove the assertion from
ibx_pch_dpll_disable, because we the dpll state tracking should
already handle this case correctly.

Changes since v1:
- Fixup accidental early return in intel_prepare_shared_dpll, oops!
Changes since v2:
- Don't use the freed crtc_state in intel_crtc_disable_noatomic()
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181005095244.1324-1-maarten.lankhorst@linux.intel.com