NFSv4.1: Fix a request leak on the back channel

commit b3b02ae5 upstream.

If the call to svc_process_common() fails, then the request
needs to be freed before we can exit bc_svc_process.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>