drm/amdgpu: fix warning in ras_debugfs_create_all()

Fix the warning
"warn: variable dereferenced before check 'obj' (see line 1131)"
by removing unnecessary checks as amdgpu_ras_debugfs_create_all()
is only called from amdgpu_debugfs_init() where obj member in
con->head list is not NULL.
Use list_for_each_entry() instead list_for_each_entry_safe() as obj
do not to be freeing or removing from list during this process.
Signed-off-by: Stanley.Yang <Stanley.Yang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c

@@ -1116,7 +1116,7 @@ void amdgpu_ras_debugfs_create(struct amdgpu_device *adev,
 void amdgpu_ras_debugfs_create_all(struct amdgpu_device *adev)
 {
 	struct amdgpu_ras *con = amdgpu_ras_get_context(adev);
-	struct ras_manager *obj, *tmp;
+	struct ras_manager *obj;
 	struct ras_fs_if fs_info;
 
 	/*
@@ -1128,10 +1128,7 @@ void amdgpu_ras_debugfs_create_all(struct amdgpu_device *adev)
 
 	amdgpu_ras_debugfs_create_ctrl_node(adev);
 
-	list_for_each_entry_safe(obj, tmp, &con->head, node) {
-		if (!obj)
-			continue;
-
+	list_for_each_entry(obj, &con->head, node) {
 		if (amdgpu_ras_is_supported(adev, obj->head.block) &&
 			(obj->attr_inuse == 1)) {
 			sprintf(fs_info.debugfs_name, "%s_err_inject",