uapi/hfi1_user: Correct comment for capability bit

The HFI1_CAP_TID_UNMAP comment was incorrectly implying the
opposite of what capability actually did. Correct this error.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>