amd/display/amdgpu_dm: delete same check in if condition

In function amdgpu_dm_connector_get_modes, drm_edid_is_valid
will check weather (!edid), no need to check again in the if
branch.
Reviewed-by: NHarry Wentland <harry.wentland@amd.com>
Signed-off-by: NBernard Zhao <bernard@vivo.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -6846,7 +6846,7 @@ static int amdgpu_dm_connector_get_modes(struct drm_connector *connector)
 
 	encoder = amdgpu_dm_connector_to_encoder(connector);
 
-	if (!edid || !drm_edid_is_valid(edid)) {
+	if (!drm_edid_is_valid(edid)) {
 		amdgpu_dm_connector->num_modes =
 				drm_add_modes_noedid(connector, 640, 480);
 	} else {