dev_table's raison d'etre was to associate an inode back to a struct
ib_uverbs_device.

However, now that we've converted ib_uverbs_device to contain an
embedded cdev (instead of a *cdev), we can use the container_of()
macro and cast back to the containing device.

There's no longer any need for dev_table, so get rid of it.
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>