drm/i915/hdcp: No HDCP when encoder is't initialized

There can be situation when DP MST connector is created without
mst modeset being done, in those cases connector->encoder will be
NULL. MST connector->encoder initializes after modeset.
Don't enable HDCP in such cases to prevent any crash.

Cc: Ramalingam C <ramalingam.c@intel.com>
Cc: Juston Li <juston.li@intel.com>
Tested-by: Karthik B S <karthik.b.s@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210111081120.28417-5-anshuman.gupta@intel.com

drivers/gpu/drm/i915/display/intel_hdcp.c

@@ -2106,6 +2106,12 @@ int intel_hdcp_enable(struct intel_connector *connector,
 	if (!hdcp->shim)
 		return -ENOENT;
 
+	if (!connector->encoder) {
+		drm_err(&dev_priv->drm, "[%s:%d] encoder is not initialized\n",
+			connector->base.name, connector->base.base.id);
+		return -ENODEV;
+	}
+
 	mutex_lock(&hdcp->mutex);
 	mutex_lock(&dig_port->hdcp_mutex);
 	drm_WARN_ON(&dev_priv->drm,