net: airoha: Fix PPE table access in airoha_ppe_debugfs_foe_show()

net: airoha: Fix PPE table access in airoha_ppe_debugfs_foe_show()

In order to avoid any possible race we need to hold the ppe_lock
spinlock accessing the hw PPE table. airoha_ppe_foe_get_entry routine is
always executed holding ppe_lock except in airoha_ppe_debugfs_foe_show
routine. Fix the problem introducing airoha_ppe_foe_get_entry_locked
routine.

Fixes: 3fe15c640f380 ("net: airoha: Introduce PPE debugfs support")
Reviewed-by: Dawid Osuchowski <dawid.osuchowski@linux.intel.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250731-airoha_ppe_foe_get_entry_locked-v2-1-50efbd8c0fd6@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>