net: altera: set a couple error code in probe()

There are two error paths which accidentally return success instead of
a negative error code.

Fixes: bbd2190c

 ("Altera TSE: Add main and header file for Altera Ethernet Driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>