gianfar: free/iounmap memory after an error in mii bus initialization

Recent changes to MII bus initialization code added exit points which
didn't free or iounmap the bus before returning.

Addresses http://bugzilla.kernel.org/show_bug.cgi?id=11372

.

Signed-off-by: Andy Fleming <afleming@freescale.com>
Reported-by: Daniel Marjamki <danielm77@spray.se>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>