rgw: need to pass need_to_wait for throttle_data()

need_to_wait wasn't passed into processor->throttle_data(). This was
broken in fix for #8937.

CID 1229541:    (PW.PARAM_SET_BUT_NOT_USED)

Backport: firefly

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
Merge pull request #2191 from ceph/wip-rgw-need-to-wait

rgw: need to pass need_to_wait for throttle_data()

Reviewed-by: Sage Weil <sage@redhat.com>