net: bcmgenet: fix bcmgenet_open()

If bcmgenet_init_dma() fails, it cleans up after itself. Rx and Tx
DMAs are off, and NAPI instances haven't been netif_napi_add()'ed.
Therefore, we need to skip calling bcmgenet_fini_dma() on the error
handling path. bcmgenet_resume() already does this correctly.

Signed-off-by: Petri Gynther <pgynther@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>