drm/dp_mst: Simplify the condition when to enumerate path resources

drm/dp_mst: Simplify the condition when to enumerate path resources

In the
	if (old_ddps != port->ddps || !created)
		if (port->ddps && !port->input)
			ret = drm_dp_send_enum_path_resources();

sequence the first if's condition is true if the port exists already
(!created) or the port was created anew (hence old_ddps==0) and it was
in the plugged state (port->ddps==1). The second if's condition is true
for output ports in the plugged state. So the function is called for an
output port in the plugged state, regardless if it already existed or
not and regardless of the old plugged state. In all other cases
port->full_pbn can be zeroed as the port is either an input for which
full_pbn is never set, or an output in the unplugged state for which
full_pbn was already zeroed previously or the port was just created
(with port->full_pbn==0).

Simplify the condition, making it clear that the path resources are
always enumerated for an output port in the plugged state.

Cc: Lyude Paul <lyude@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240722165503.2084999-4-imre.deak@intel.com