net/fsl_pq_mdio: use spin_event_timeout() to poll the indicator register

Macro spin_event_timeout() was designed for simple polling of hardware
registers with a timeout, so use it when we poll the MIIMIND register.
This allows us to return an error code instead of polling indefinitely.

Note that PHY_INIT_TIMEOUT is a count of loop iterations, so we can't use
it for spin_event_timeout(), which asks for microseconds.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>