etraxfs_eth: Don't use hw_error() in init() method

Device init() methods aren't supposed to call hw_error(), they should
report the error and fail cleanly.  Do that.

Cc: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-Id: <1450370121-5768-5-git-send-email-armbru@redhat.com>