When doing a software reset, the reset flag should be written without
other bits set. Writing the current state will lead to restoring the
state of the PHY (e.g. Powerdown), which is not what is expected from
a software reset.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Michael Welling <mwelling@ieee.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>