In alloc_thread_groups, worker_groups is a pointer to an array,
not an array of pointers.
So
   worker_groups[i]
is wrong.  It should be
   &(*worker_groups)[i]

Found-by: coverity
Fixes: 60aaf933Reported-by: NBen Hutchings <bhutchings@solarflare.com>
Cc: majianpeng <majianpeng@gmail.com>
Signed-off-by: NNeilBrown <neilb@suse.de>