[CIFS] fix mempool destroy done in wrong order in cifs error path

Slab cache used as memory pool can not be destroyed before the memory
pool destruction. Because the memory pool still holds some objects and
kmem_cache_destroy() says "Can't free all objects".

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>