net: dsa: LAN9303: Add early read to sync

Add initial BYTE_ORDER read to sync the 32-bit accesses over the 16-bit
mdio bus to improve driver robustness.

The lan9303 expects two mdio read transactions back-to-back to read a
32-bit register. The first read transaction causes the other half of the
32-bit register to get latched.  The subsequent read returns the latched
second half of the 32-bit read. The BYTE_ORDER register is an exception to
this rule. As it is a constant value, there is no need to latch the second
half. We read this register first in case there were reads during the boot
loader process that might have occurred prior to this driver taking over
ownership of accessing this device.

This patch has been tested on the SAMA5D3-EDS with a LAN9303 RMII daughter
card.

Signed-off-by: Jerry Ray <jerry.ray@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>