net: axienet: Fix error return code in axienet_probe()

In the DMA memory resource get failed case, the error is not
set and 0 will be returned. Fix it by removing redundant check
since devm_ioremap_resource() will handle it.

Fixes: 28ef9ebd

 ("net: axienet: make use of axistream-connected attribute optional")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>