of_mdio: fix kernel-doc for of_phy_connect()

The 'flags' parameter of the of_phy_connect() function wasn't described
in  the kernel-doc comment...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>