CVE-2022-48841 ice: fix NULL pointer dereference in ice_update_vsi_tx_ring_stats()

In the Linux kernel, the following vulnerability has been resolved:

ice: fix NULL pointer dereference in ice_update_vsi_tx_ring_stats()

It is possible to do NULL pointer dereference in routine that updates
Tx ring stats. Currently only stats and bytes are updated when ring
pointer is valid, but later on ring is accessed to propagate gathered Tx
stats onto VSI stats.

Change the existing logic to move to next ring when ring is NULL.