mdio: aspeed: Fix "Link is Down" issue

The issue happened randomly in runtime.  The message "Link is Down" is
popped but soon it recovered to "Link is Up".

The "Link is Down" results from the incorrect read data for reading the
PHY register via MDIO bus.  The correct sequence for reading the data
shall be:
1. fire the command
2. wait for command done (this step was missing)
3. wait for data idle
4. read data from data register

Cc: stable@vger.kernel.org
Fixes: f160e994 ("net: phy: Add mdio-aspeed")
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20211125024432.15809-1-dylan_hung@aspeedtech.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>