fix warning in fs/dlm/netlink.c

this warning:

  fs/dlm/netlink.c: In function ‘dlm_timeout_warn’:
  fs/dlm/netlink.c:131: warning: ‘send_skb’ may be used uninitialized in this function

triggers because GCC does not recognize the (correct) error flow
between prepare_data() and send_skb.

Annotate it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>