IB/uverbs: Do not pass struct ib_device to the ioctl methods

This does the same as the patch before, except for ioctl. The rules are
the same, but for the ioctl methods the core code handles setting up the
uobject.

- Retrieve the ib_dev from the uobject->context->device. This is
  safe under ioctl as the core has already done rdma_alloc_begin_uobject
  and so CREATE calls are entirely protected by the rwsem.
- Retrieve the ib_dev from uobject->object
- Call ib_uverbs_get_ucontext()

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>