net: ethernet: mediatek: fix incorrect return value of devm_clk_get with EPROBE_DEFER

1) If the return value of devm_clk_get is EPROBE_DEFER, we should
defer probing the driver. The change is verified and works based
on 4.8-rc1 staying with the latest clk-next code for MT7623.
2) Changing with the usage of loops to work out if all clocks
required are fine

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>