MediaMetrics: fix error for compiler update.

frameworks/av/services/mediametrics/TransactionLog.h:161:19:
  error: declaration shadows a structured binding [-Werror,-Wshadow]
            auto [s, l] = dumpMapTimeItem(it->second, ll - 1, sinceNs, prefix);
                  ^

Bug: 193903230
Test: build with the next compiler
Change-Id: Ib9cc931d97f16f7b85b987baaed280802a0f5c8b