simpleperf: Fix dumping build id for system wide etm recording

For a bug introduced in aosp/3155713, build ids are not dumped
for mmap records stored in init_map feature section.

Bug: 361638495
Test: run simpleperf_unit_test
Change-Id: I575045a2b2ea1d1f071a01201889d85df8d1248f
4 files changed