vhost: fix crash after mmap failure
vhost: fix crash after mmap failure

If mmap() call fails in vhost_user_set_mem_table, dev->mem
is set to NULL. If later, qva_to_vva() is called, a segfault
occurs.

Fixes: 8f972312b8f4 ("vhost: support vhost-user")
Cc: stable@dpdk.org

Reviewed-by: Tiwei Bie <f338cf29d7d69ff1bc99f755ebfb0eb0accd409e@intel.com>
Signed-off-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>
Reviewed-by: Jens Freimann <ca9361fbe2c56b38bfc6f0fa839493a196cfbd8f@redhat.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk