net: ethernet: ti: remove redundant NULL check.

cpdma_chan_destroy() on a NULL pointer is a no-op, so the NULL check in
cpdma_ctlr_destroy() can safely be removed.

Signed-off-by: Cyril Roelandt <tipecaml@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>