devlink: Warn on resource ID collision with PARENT_TOP

devlink: Warn on resource ID collision with PARENT_TOP

ID 0 serves as the sentinel DEVLINK_RESOURCE_ID_PARENT_TOP to mark
top-level resources. While it is technically possible to use 0 as a real
resource ID, a user might be tempted to write:

enum {
    MY_RESOURCE_ID_A,  /* == DEVLINK_RESOURCE_ID_PARENT_TOP ! */
    MY_RESOURCE_ID_B,
    MY_RESOURCE_ID_C,
    MY_RESOURCE_ID_D,
    ...
};

register(..., MY_RESOURCE_ID_C, DEVLINK_RESOURCE_ID_PARENT_TOP, ...);
register(..., MY_RESOURCE_ID_D, MY_RESOURCE_ID_C, ...);
/* D is a child of C */

register(..., MY_RESOURCE_ID_A, DEVLINK_RESOURCE_ID_PARENT_TOP, ...);
register(..., MY_RESOURCE_ID_B, MY_RESOURCE_ID_A, ...);
/* Is B intentionally top-level, or is it actually a child of A? */

Add a WARN_ON() to catch this and prevent confusion.

Signed-off-by: David Yang <mmyangfl@gmail.com>
Link: https://patch.msgid.link/20260611070856.889700-6-mmyangfl@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>