IB/umad: Remove port_table[]

We no longer need this data structure, as it was used to associate an
inode back to a struct ib_umad_port during ->open().  But now that
we're embedding a struct cdev in struct ib_umad_port, we can use the
container_of() macro to go from the inode back to the device instead.

Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>