ibmvnic: free tx_pool if tso_pool alloc fails

Free tx_pool and clear it, if allocation of tso_pool fails.

release_tx_pools() assumes we have both tx and tso_pools if ->tx_pool is
non-NULL. If allocation of tso_pool fails in init_tx_pools(), the assumption
will not be true and we would end up dereferencing ->tx_buff, ->free_map
fields from a NULL pointer.

Fixes: 3205306c ("ibmvnic: Update TX pool initialization routine")
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>