RDMA/siw: Fix refcounting leak in siw_create_qp()

The atomic_inc() needs to be paired with an atomic_dec() on the error
path.

Fixes: 514aee66 ("RDMA: Globally allocate and release QP memory")
Link: https://lore.kernel.org/r/20220118091104.GA11671@kili


Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>