According to Documentation/driver-api/usb/URB.rst when a device
is unplugged usb_submit_urb() returns -ENODEV.

This error code propagates all the way up to usbnet_read_cmd() and
usbnet_write_cmd() calls inside the smsc95xx.c driver during
Ethernet cable unplug, unbind or reboot.

This causes the following errors to be shown on reboot, for example:

ci_hdrc ci_hdrc.1: remove, state 1
usb usb2: USB disconnect, device number 1
usb 2-1: USB disconnect, device number 2
usb 2-1.1: USB disconnect, device number 3
smsc95xx 2-1.1:1.0 eth1: unregister 'smsc95xx' usb-ci_hdrc.1-1.1, smsc95xx USB 2.0 Ethernet
smsc95xx 2-1.1:1.0 eth1: Failed to read reg index 0x00000114: -19
smsc95xx 2-1.1:1.0 eth1: Error reading MII_ACCESS
smsc95xx 2-1.1:1.0 eth1: __smsc95xx_mdio_read: MII is busy
smsc95xx 2-1.1:1.0 eth1: Failed to read reg index 0x00000114: -19
smsc95xx 2-1.1:1.0 eth1: Error reading MII_ACCESS
smsc95xx 2-1.1:1.0 eth1: __smsc95xx_mdio_read: MII is busy
smsc95xx 2-1.1:1.0 eth1: hardware isn't capable of remote wakeup
usb 2-1.4: USB disconnect, device number 4
ci_hdrc ci_hdrc.1: USB bus 2 deregistered
ci_hdrc ci_hdrc.0: remove, state 4
usb usb1: USB disconnect, device number 1
ci_hdrc ci_hdrc.0: USB bus 1 deregistered
imx2-wdt 30280000.watchdog: Device shutdown: Expect reboot!
reboot: Restarting system

Ignore the -ENODEV errors inside __smsc95xx_mdio_read() and
__smsc95xx_phy_wait_not_busy() and do not print error messages
when -ENODEV is returned.

Fixes: a049a30f ("net: usb: Correct PHY handling of smsc95xx")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>