RDMA: Fix double-free in srq creation error flow

RDMA: Fix double-free in srq creation error flow

The cited commit introduced a double-free of the srq buffer in the error
flow of procedure __uverbs_create_xsrq().

The problem is that ib_destroy_srq_user() called in the error flow also
frees the srq buffer.

Thus, if uverbs_response() fails in __uverbs_create_srq(), the srq buffer
will be freed twice.

Cc: <stable@vger.kernel.org>
Fixes: 8a786e14991b ("RDMA: Handle SRQ allocations by IB/core")
Link: https://lore.kernel.org/r/20190916071154.20383-5-leon@kernel.org
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>