net: macb: simplify clk_init with dev_err_probe

On some platforms, e.g., the ZynqMP, devm_clk_get can return
-EPROBE_DEFER if the clock controller, which is implemented in firmware,
has not been probed yet.

As clk_init is only called during probe, use dev_err_probe to simplify
the error message and hide it for -EPROBE_DEFER.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>