sctp: remove the useless check in sctp_renege_events

Remove the 'if (chunk)' check in sctp_renege_events for idata process,
as all renege commands are generated in sctp_eat_data and it can't be
NULL.

The same thing we already did for common data in sctp_ulpq_renege.

Fixes: 94014e8d

 ("sctp: implement renege_events for sctp_stream_interleave")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>