rxrpc: Fix a missing rxrpc_put_peer() in the error_report handler

Fix a missing call to rxrpc_put_peer() on the main path through the
rxrpc_error_report() function.  This manifests itself as a ref leak
whenever an ICMP packet or other error comes in.

In commit f3344303, the hand-off of the ref to a work item was removed
and was not replaced with a put.

Fixes: f3344303 ("rxrpc: Fix error distribution")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>