net: phy: fixed_phy: Remove unused seqcount

Commit bf7afb29 ("phy: improve safety of fixed-phy MII register
reading") protected the fixed PHY status with a sequence counter.

Two years later, commit d2b97793

 ("net: phy: fixed-phy: remove
fixed_phy_update_state()") removed the sequence counter's write side
critical section -- neutralizing its read side retry loop.

Remove the unused seqcount.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>