drm/radeon: remove set but not used variable 'dig_connector'

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

drivers/gpu/drm/radeon/atombios_dp.c: In function radeon_dp_get_panel_mode:
drivers/gpu/drm/radeon/atombios_dp.c:415:36: warning: variable dig_connector set but not used [-Wunused-but-set-variable]

It is not used since commit 379dfc25 ("drm/radeon/dp:
switch to the common i2c over aux code")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/atombios_dp.c

@@ -412,7 +412,6 @@ int radeon_dp_get_panel_mode(struct drm_encoder *encoder,
 	struct drm_device *dev = encoder->dev;
 	struct radeon_device *rdev = dev->dev_private;
 	struct radeon_connector *radeon_connector = to_radeon_connector(connector);
-	struct radeon_connector_atom_dig *dig_connector;
 	int panel_mode = DP_PANEL_MODE_EXTERNAL_DP_MODE;
 	u16 dp_bridge = radeon_connector_encoder_get_dp_bridge_encoder_id(connector);
 	u8 tmp;
@@ -423,8 +422,6 @@ int radeon_dp_get_panel_mode(struct drm_encoder *encoder,
 	if (!radeon_connector->con_priv)
 		return panel_mode;
 
-	dig_connector = radeon_connector->con_priv;
-
 	if (dp_bridge != ENCODER_OBJECT_ID_NONE) {
 		/* DP bridge chips */
 		if (drm_dp_dpcd_readb(&radeon_connector->ddc_bus->aux,