IB/rdmavt: Insure QP vmalloc variants zero memory

The usage of the various vmalloc APIs do not consistently zero memory
when allocating the swqe. Insure zeroing variants are used.

Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>