net: airoha: Always check return value from airoha_ppe_foe_get_entry()

airoha_ppe_foe_get_entry routine can return NULL, so check the returned
pointer is not NULL in airoha_ppe_foe_flow_l2_entry_update()

Fixes: b81e0f2b ("net: airoha: Add FLOW_CLS_STATS callback support")
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250618-check-ret-from-airoha_ppe_foe_get_entry-v2-1-068dcea3cc66@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>