sunrpc: fix error path in module_init

register_rpc_pipefs() needs to clean up rpc_inode_cache
by kmem_cache_destroy() on register_filesystem() failure.

init_sunrpc() needs to unregister rpc_pipe_fs by unregister_rpc_pipefs()
when rpc_init_mempool() returns error.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>