net: pcs: xpcs: rename xpcs_get_id()

Rename xpcs_get_id() to xpcs_read_id() which more closely reflects
the purpose of this function.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>