IB/uverbs: Do not check for device disassociation during ioctl

Now that the ioctl path and uobjects are converted to use uverbs_api, it
is now safe to remove the disassociation protection from the common ioctl
code.

This completes the work to make destroy functions continue to work even
after device disassociation.

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