at91ether: return PTR_ERR if call to clk_get fails

we are currently returning ENODEV, as the clk_get may give a exact
error code in its returned pointer, assign it to the ret by using the
PTR_ERR function, so that the subsequent goto label will jump to the
error path and clean the driver and return the error correctly.

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>