net: fec: use device sequence vs index when fetching fec

net: fec: use device sequence vs index when fetching fec

When using uclass_get_device* to get the FEC device we need to use
device sequence instead of index into UCLASS_ETH. In systems where for
example a I2C based DSA switch exists it will probe before the FEC
master and its ports will be registered first and have the first
indexes yet the FEC's sequence comes from the device-tree alias.

Take for example the imx8mm-venice-gw7901 board which has an i2c based
DSA switch:

u-boot=> net list
eth1 : lan1 00:0d:8d:aa:00:2f
eth2 : lan2 00:0d:8d:aa:00:30
eth3 : lan3 00:0d:8d:aa:00:31
eth4 : lan4 00:0d:8d:aa:00:32
eth0 : ethernet@30be0000 00:0d:8d:aa:00:2e active

Thus in this case uclass_get_device(UCLASS_ETH, 0, &dev) returns lan1
which is wrong but uclass_get_device_seq(UCLASS_ETH, 0, &dev) returns
ethernet@30be000 which is correct.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>