SUNRPC: De-duplicate .pc_release() call sites

There was some spaghetti in svc_process_common() that had evolved
over time such that there was still one case that needed a call
to .pc_release() but never made it. That issue was removed in
the previous patch.

As additional insurance against missing this important callout,
ensure that the .pc_release() method is always called, no matter
what the reply_stat is.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>