net: bcm4908: Handle dma_set_coherent_mask error codes

The return value of dma_set_coherent_mask() is not always 0.
To catch the exception in case that dma is not support the mask.

Fixes: 9d61d138

 ("net: broadcom: rename BCM4908 driver & update DT binding")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>