net: ravb: Fix GbEth jumbo packet RX checksum handling

net: ravb: Fix GbEth jumbo packet RX checksum handling

Sending a 7kB ping packet to the RZ/G2L in v6.9-rc2 causes the following
backtrace:

	WARNING: CPU: 0 PID: 0 at include/linux/skbuff.h:3127 skb_trim+0x30/0x38
	Hardware name: Renesas SMARC EVK based on r9a07g044l2 (DT)
	pc : skb_trim+0x30/0x38
	lr : ravb_rx_csum_gbeth+0x40/0x90
	Call trace:
	 skb_trim+0x30/0x38
	 ravb_rx_gbeth+0x56c/0x5cc
	 ravb_poll+0xa0/0x204
	 __napi_poll+0x38/0x17c

This is caused by ravb_rx_gbeth() calling ravb_rx_csum_gbeth() with the
wrong skb for a packet which spans multiple descriptors. To fix this,
use the correct skb.

Fixes: c2da9408579d ("ravb: Add Rx checksum offload support for GbEth")
Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>