phy: mdio-cavium: Add missing MODULE_* annotations.

When the code was factored out of mdio-octeon.c, the
MODULE_DESCRIPTION, MODULE_AUTHOR and MODULE_LICENSE annotations were
inadvertently omitted.  Restore them so that we don't get kernel taint
warnings upon module loading.

Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>