net: pse-pd: tps23881: Clarify setup_pi_matrix callback documentation

Improve the setup_pi_matrix callback documentation to clarify its purpose
and usage. The enhanced description explains that PSE PI devicetree nodes
are pre-parsed before this callback is invoked, and drivers should utilize
pcdev->pi[x]->pairset[y].np to map PSE controller hardware ports to their
corresponding Power Interfaces.

This clarification helps driver implementers understand the callback's
role in establishing the hardware-to-PI relationship mapping.

Signed-off-by: Kory Maincent <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

include/linux/pse-pd/pse.h

···
 /**
  * struct pse_controller_ops - PSE controller driver callbacks
  *
- * @setup_pi_matrix: setup PI matrix of the PSE controller
+ * @setup_pi_matrix: Setup PI matrix of the PSE controller.
+ *		     The PSE PIs devicetree nodes have already been parsed by
+ *		     of_load_pse_pis() and the pcdev->pi[x]->pairset[y].np
+ *		     populated. This callback should establish the
+ *		     relationship between the PSE controller hardware ports
+ *		     and the PSE Power Interfaces, either through software
+ *		     mapping or hardware configuration.
  * @pi_get_admin_state: Get the operational state of the PSE PI. This ops
  *			is mandatory.
  * @pi_get_pw_status: Get the power detection status of the PSE PI. This