RDMA/iwcm: Fix iwcm work deallocation

The dealloc_work_entries() function must update the work_free_list pointer
while freeing its entries, since potentially called again on same list. A
second iteration of the work list caused system crash. This happens, if
work allocation fails during cma_iw_listen() and free_cm_id() tries to
free the list again during cleanup.

Fixes: 922a8e9f

 ("RDMA: iWARP Connection Manager.")
Link: https://lore.kernel.org/r/20200302181614.17042-1-bmt@zurich.ibm.com
Reported-by:  <syzbot+cb0c054eabfba4342146@syzkaller.appspotmail.com>
Signed-off-by: Bernard Metzler <bmt@zurich.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>