ixp4xx_eth: Fix up the get_ts_info ethtool method.

Commit e77bd1ec121ee4163a6b42a44e87b2e382c39e04 added support for a
new ethtool function, but that cannot compile due to a misnamed global
variable. Not that it really matters (since the IXP4xx does compile
either, as of about Linux 3.1) but just in case, this patch fixes the
misnamed variable in the PHC driver.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>