drm/i915/icl: fix icl_unmap/map_plls_to_ports

All connectors may not have best_encoder attached, so don't dereference
encoder pointer for each connector.

Fixes: c27e917e2b ("drm/i915/icl: add basic support for the ICL clocks")
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180525155238.7054-1-lucas.demarchi@intel.com
(cherry picked from commit c46ef57d20)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_ddi.c

@@ -2453,12 +2453,13 @@ void icl_map_plls_to_ports(struct drm_crtc *crtc,
 	for_each_new_connector_in_state(old_state, conn, conn_state, i) {
 		struct intel_encoder *encoder =
 			to_intel_encoder(conn_state->best_encoder);
-		enum port port = encoder->port;
+		enum port port;
 		uint32_t val;
 
 		if (conn_state->crtc != crtc)
 			continue;
 
+		port = encoder->port;
 		mutex_lock(&dev_priv->dpll_lock);
 
 		val = I915_READ(DPCLKA_CFGCR0_ICL);
@@ -2490,11 +2491,12 @@ void icl_unmap_plls_to_ports(struct drm_crtc *crtc,
 	for_each_old_connector_in_state(old_state, conn, old_conn_state, i) {
 		struct intel_encoder *encoder =
 			to_intel_encoder(old_conn_state->best_encoder);
-		enum port port = encoder->port;
+		enum port port;
 
 		if (old_conn_state->crtc != crtc)
 			continue;
 
+		port = encoder->port;
 		mutex_lock(&dev_priv->dpll_lock);
 		I915_WRITE(DPCLKA_CFGCR0_ICL,
 			   I915_READ(DPCLKA_CFGCR0_ICL) |