net: ethernet: stmmac: Enable interface clocks on probe for IPQ806x

[ Upstream commit a96ac8a0045e3cbe3e5af6d1b3c78c6c2065dec5 ]

The ipq806x_gmac_probe() function enables the PTP clock but not the
appropriate interface clocks. This means that if the bootloader hasn't
done so attempting to bring up the interface will fail with an error
like:

[   59.028131] ipq806x-gmac-dwmac 37600000.ethernet: Failed to reset the dma
[   59.028196] ipq806x-gmac-dwmac 37600000.ethernet eth1: stmmac_hw_setup: DMA engine initialization failed
[   59.034056] ipq806x-gmac-dwmac 37600000.ethernet eth1: stmmac_open: Hw setup failed

This patch, a slightly cleaned up version of one posted by Sergey
Sergeev in:

https://forum.openwrt.org/t/support-for-mikrotik-rb3011uias-rm/4064/257



correctly enables the clock; we have already configured the source just
before this.

Tested on a MikroTik RB3011.

Signed-off-by: Jonathan McDowell <noodles@earth.li>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>