perf/bpf: Reorder bpf_overflow_handler() ahead of __perf_event_overflow()

This will allow __perf_event_overflow() to call bpf_overflow_handler().

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240412015019.7060-2-khuey@kylehuey.com