net: ks8851: Clean up chip ID readout

There is only one chip ID in the table of chip IDs for this chip.
Read out the chip ID instead and mask off the last "revision" bit
to check the chip ID, this works for all chips in the family. Then
drop the chip ID passing around.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Eugen Hristev <eugen.hristev@microchip.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>