net: asix: Move declaration of ax88172a_info to shared header

Ensure that the definition of ax88172a_info matches the declaration seen
by users and silence sparse warnings about symbols without declarations
in the global namespace by moving the declaration into the shared header
asix.h.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>