IB/ucm: Fix bitmap wrap when devnum > IB_UCM_MAX_DEVICES

ib_ucm_release_dev clears the wrong bit if devnum is greater
than IB_UCM_MAX_DEVICES.

Signed-off-by: Carol L Soto <clsoto@linux.vnet.ibm.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>