AFS: Use patched rxrpc_kernel_send_data() correctly

Fix afs_send_simple_reply() to accept a greater-than-zero return value from
rxrpc_kernel_send_data() as being a successful return rather than thinking it
an error and aborting the call.

rxrpc_kernel_send_data() previously returned zero incorrectly when it worked
successfully, but has been patched to return the number of bytes it
transmitted.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>