i40iw: Fix double free of QP

A QP can be double freed if i40iw_cm_disconn() is
called while it is currently being freed by
i40iw_rem_ref(). The fix in i40iw_cm_disconn() will
first check if the QP is already freed before
making another request for the QP to be freed.

Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Henry Orosco <henry.orosco@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>