drm/i915: Remove set but not used variable 'encoder'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/i915/display/intel_dp.c: In function 'intel_dp_set_drrs_state':
drivers/gpu/drm/i915/display/intel_dp.c:6623:24: warning:
 variable 'encoder' set but not used [-Wunused-but-set-variable]

It's never used, so can be removed.Also remove related
variable 'dig_port'
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190705113112.64715-1-yuehaibing@huawei.com

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

@@ -6620,8 +6620,6 @@ static void intel_dp_set_drrs_state(struct drm_i915_private *dev_priv,
 				    const struct intel_crtc_state *crtc_state,
 				    int refresh_rate)
 {
-	struct intel_encoder *encoder;
-	struct intel_digital_port *dig_port = NULL;
 	struct intel_dp *intel_dp = dev_priv->drrs.dp;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc_state->base.crtc);
 	enum drrs_refresh_rate_type index = DRRS_HIGH_RR;
@@ -6636,9 +6634,6 @@ static void intel_dp_set_drrs_state(struct drm_i915_private *dev_priv,
 		return;
 	}
 
-	dig_port = dp_to_dig_port(intel_dp);
-	encoder = &dig_port->base;
-
 	if (!intel_crtc) {
 		DRM_DEBUG_KMS("DRRS: intel_crtc not initialized\n");
 		return;