rdma: fix buggy code that the compiler warns about

rdma: fix buggy code that the compiler warns about

Get rid of this warning:

  drivers/infiniband/sw/rdmavt/cq.c: In function ‘rvt_cq_exit’:
  drivers/infiniband/sw/rdmavt/cq.c:542:2: warning: ‘worker’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    kthread_destroy_worker(worker);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

by fixing the function to actually work.

Fixes: 38c2969ef89f ("IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker")
Cc: Petr Mladek <pmladek@suse.com>
Cc: Doug Ledford <dledford@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>