drm/ast: open key before detect chips

Some config settings like 3rd TX chips will not get correctly
if the extended reg is protected

Signed-off-by: Y.C. Chen <yc_chen@aspeedtech.com>
Reviewed-by: Egbert Eich <eich@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ast/ast_main.c

@@ -67,6 +67,7 @@ static int ast_detect_chip(struct drm_device *dev)
 {
 	struct ast_private *ast = dev->dev_private;
 	uint32_t data, jreg;
+	ast_open_key(ast);
 
 	if (dev->pdev->device == PCI_CHIP_AST1180) {
 		ast->chip = AST1100;