ibmvnic: Potential NULL dereference in clean_one_tx_pool()

There is an && vs || typo here, which potentially leads to a NULL
dereference.

Fixes: e9e1e978

 ("ibmvnic: Update TX pool cleaning routine")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>