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/BufferInfoMaliMediatek.cpp b/bufferinfo/legacy/BufferInfoMaliMediatek.cpp
index 2e10460..6dac973 100644
--- a/bufferinfo/legacy/BufferInfoMaliMediatek.cpp
+++ b/bufferinfo/legacy/BufferInfoMaliMediatek.cpp
@@ -38,7 +38,7 @@
   if (!hnd)
     return {};
 
-  uint32_t fmt = ConvertHalFormatToDrm(hnd->req_format);
+  const uint32_t fmt = ConvertHalFormatToDrm(hnd->req_format);
   if (fmt == DRM_FORMAT_INVALID)
     return {};