net: bcmgenet: remove __bcmgenet_fini_dma()

bcmgenet_fini_dma() is the only caller of __bcmgenet_fini_dma().
Move __bcmgenet_fini_dma() code inside bcmgenet_fini_dma().

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