trivial: etraxfs_eth: Eliminate checkpatch errors

This is a trivial patch to harmonize the coding style on
hw/etraxfs_eth.c. This is in preparation to split off the bitbang mdio
code into a separate file.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Paul Brook <paul@codesourcery.com>
Cc: Edgar E. Iglesias <edgar.iglesias@gmail.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>
Cc: Andreas Färber <afaerber@suse.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>