net: micrel: Fix the frequency adjustments

By default lan8841's 1588 clock frequency is 125MHz. But when adjusting
the frequency, it is using the 1PPM format of the lan8814. Which is the
wrong format as lan8814 has a 1588 clock frequency of 250MHz. So then
for each 1PPM adjustment would adjust less than expected.
Therefore fix this by using the correct 1PPM format for lan8841.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>