net: cavium: liquidio: fix check for in progress flag

smatch detected a suspicious looking bitop condition:

drivers/net/ethernet/cavium/liquidio/lio_main.c:2529
  handle_timestamp() warn: suspicious bitop condition

(skb_shinfo(skb)->tx_flags | SKBTX_IN_PROGRESS is always non-zero,
so the logic is definitely not correct.  Use & to mask the correct
bit.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>