net/fsl_pq_mdio: merge some functions together

A few small functions were called only by other functions in the same
file, so merge them together.  One function, for example, was calculating
the device address even though the caller was doing the same thing.

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