drm/gma500: Fix end of loop tests for list_for_each_entry

stable inclusion
from stable-5.10.65
commit 3d58f5e83f97f2e732c3a00949a935e601d42529
bugzilla: 182361 https://gitee.com/openeuler/kernel/issues/I4EH3U

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d58f5e83f97f2e732c3a00949a935e601d42529

--------------------------------

[ Upstream commit ea9a897b ]

The list_for_each_entry() iterator, "connector" in this code, can never be
NULL.  If we exit the loop without finding the correct  connector then
"connector" points invalid memory that is an offset from the list head.
This will eventually lead to memory corruption and presumably a kernel
crash.

Fixes: 9bd81acd ("gma500: Convert Oaktrail to work with new output handling")
Signed-off-by: NHarshvardhan Jha <harshvardhan.jha@oracle.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210709073959.11443-1-harshvardhan.jha@oracle.comSigned-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/gpu/drm/gma500/oaktrail_lvds.c

@@ -117,7 +117,7 @@ static void oaktrail_lvds_mode_set(struct drm_encoder *encoder,
 			continue;
 	}
 
-	if (!connector) {
+	if (list_entry_is_head(connector, &mode_config->connector_list, head)) {
 		DRM_ERROR("Couldn't find connector when setting mode");
 		gma_power_end(dev);
 		return;