net: ethernet: qlogic: set error code on failure

When calling dma_mapping_error(), the value of return variable rc is 0.
And when the call returns an unexpected value, rc is not set to a
negative errno. Thus, it will return 0 on the error path, and its
callers cannot detect the bug. This patch fixes the bug, assigning
"-ENOMEM" to err.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=189041

Signed-off-by: Pan Bian <bianpan2016@163.com>
Acked-by: Yuval Mintz <Yuval.Mintz@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>