perf: Fixup SIGTRAP and sample_flags interaction

The perf_event_attr::sigtrap functionality relies on data->addr being
set. However commit 7b084630 ("perf: Use sample_flags for addr")
changed this to only initialize data->addr when not 0.

Fixes: 7b084630

 ("perf: Use sample_flags for addr")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/Y3426b4OimE%2FI5po%40hirez.programming.kicks-ass.net