fsl/fman: double free on probe failure

"priv" is allocated with devm_kzalloc() so freeing it here with kfree()
will lead to a double free.

Fixes: 39339616 ('fsl/fman: Add FMan MAC driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>