CVE-2026-31501: net: ti: icssg-prueth: fix use-after-free of CPPI descriptor in RX path

In the Linux kernel, the following vulnerability has been resolved: net: ti: icssg-prueth: fix use-after-free of CPPI descriptor in RX path cppi5_hdesc_get_psdata() returns a pointer into the CPPI descriptor. In both emac_rx_packet() and emac_rx_packet_zc(), the descriptor is freed via k3_cppi_desc_pool_free() before the psdata pointer is used by emac_rx_timestamp(), which dereferences psdata[0] and psdata[1]. This constitutes a use-after-free on every received packet that goes through the timestamp path. Defer the descriptor free until after all accesses through the psdata pointer are complete. For emac_rx_packet(), move the free into the requeue label so both early-exit and success paths free the descriptor after all accesses are done. For emac_rx_packet_zc(), move the free to the end of the loop body after emac_dispatch_skb_zc() (which calls emac_rx_timestamp()) has returned.