net: macb: set MACB_CAPS_USRIO_DISABLED if no usrio config is provided

net: macb: set MACB_CAPS_USRIO_DISABLED if no usrio config is provided

bp->usrio is copied directly from dt_conf->usrio in macb_probe().

If dt_conf->usrio is NULL, we do not want to land in USRIO write
codepaths which dereference bp->usrio. Inherit automatically
MACB_CAPS_USRIO_DISABLED to avoid those.

This means a macb_config that wants to disable usrio can simply drop
its .usrio field, rather than add the disabled capability explicitly.

Nit: drop the dt_conf NULL check because the pointer is always valid.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260325-husband-cape-ec4945b9184c@spud
Signed-off-by: Jakub Kicinski <kuba@kernel.org>