drm_hwcomposer: Enable performance-avoid-endl clang-tidy check

And fix every related warning.

Change-Id: I6afacef19ac04269245ef687762698be057d420b
Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/.ci/Makefile b/.ci/Makefile
index 56d2488..ca0daca 100644
--- a/.ci/Makefile
+++ b/.ci/Makefile
@@ -56,7 +56,6 @@
     -readability-math-missing-parentheses               \
     -readability-avoid-unconditional-preprocessor-if    \
     -modernize-type-traits                              \
-    -performance-avoid-endl                             \
 
 TIDY_CHECKS_NORMAL :=                                   \
     $(TIDY_CHECKS_FINE)                                 \
diff --git a/tests/uevent_print.cpp b/tests/uevent_print.cpp
index 6ffbbfb..cfe2191 100644
--- a/tests/uevent_print.cpp
+++ b/tests/uevent_print.cpp
@@ -7,7 +7,7 @@
 int main() {
   auto uevent = android::UEvent::CreateInstance();
   if (!uevent) {
-    std::cout << "Can't initialize UEvent class" << std::endl;
+    std::cout << "Can't initialize UEvent class\n";
     return -ENODEV;
   }
 
@@ -18,8 +18,8 @@
       continue;
     }
 
-    std::cout << "New event #" << number++ << std::endl
-              << *msg << std::endl
-              << std::endl;
+    std::cout << "New event #" << number++ << '\n'
+              << *msg << '\n'
+              << std::flush;
   }
 }