dpaa_eth: Fix comparing pointer to 0

Fixes coccicheck warning:
./drivers/net/ethernet/freescale/dpaa/dpaa_eth.c:2110:30-31:
WARNING comparing pointer to 0

Avoid pointer type value compared to 0.

Signed-off-by: Aishwarya Ramakrishnan <aishwaryarj100@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>