drm_hwcomposer: CI: Bump-up clang toolchain to v15

Address new clang-tidy findings, in most cases 'misc-const-correctness'
check was addressed by adding 'const' modifier, or in some cases changed
to 'auto' (where it's better for formatting).

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/bufferinfo/legacy/BufferInfoLibdrm.cpp b/bufferinfo/legacy/BufferInfoLibdrm.cpp
index ac71ec0..b314bdc 100644
--- a/bufferinfo/legacy/BufferInfoLibdrm.cpp
+++ b/bufferinfo/legacy/BufferInfoLibdrm.cpp
@@ -154,7 +154,7 @@
   if (num_fds == 1) {
     bo->prime_fds[2] = bo->prime_fds[1] = bo->prime_fds[0];
   } else {
-    int expected_planes = (ycbcr.chroma_step == 2) ? 2 : 3;
+    const int expected_planes = (ycbcr.chroma_step == 2) ? 2 : 3;
     if (num_fds != expected_planes)
       return false;
   }