[PATCH] tulip: add return to ULI526X clause in tulip_mdio_write

The 'if' clause for ULI526X in tulip_mdio_write allows for
spin_unlock_irqrestore to be called twice for tp->mii_lock.  I believe
this is caused by the unintentional omission of a return at the end
of that clause.  This patch adds that return.

Signed-off-by: John W. Linville <linville@tuxdriver.com>