Suppress error log when timerslack_ns write fails for already dead process

lmkd uses set_sched_priority to expedite killing of its victims and this
sometimes results in timerslack_ns writes for an process which is already
dead. These messages are detrimental during troubleshooting and do not
indicate a real problem, therefore need to be suppressed.

Bug: 124324891
Test: lmkd_unit_test

Change-Id: I5bc071b47d386c279dd9a56eee51dba7797f4520
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
diff --git a/libprocessgroup/task_profiles.cpp b/libprocessgroup/task_profiles.cpp
index 447852d..b69103c 100644
--- a/libprocessgroup/task_profiles.cpp
+++ b/libprocessgroup/task_profiles.cpp
@@ -90,6 +90,10 @@
     if (sys_supports_timerslack) {
         auto file = StringPrintf("/proc/%d/timerslack_ns", tid);
         if (!WriteStringToFile(std::to_string(slack_), file)) {
+            if (errno == ENOENT) {
+                // This happens when process is already dead
+                return true;
+            }
             PLOG(ERROR) << "set_timerslack_ns write failed";
         }
     }