default: update drm_hwcomposer

Update drm_hwcomposer to the lastest upstream version:
a8ef39578ca8 (Merge "Merge remote-tracking branch 'aosp/upstream-main' into uprev" into main, 2025-01-05)

This fixes the 2 following VTS issues:
module: VtsHalGraphicsComposer3_TargetTest
testcase: PerInstance/GraphicsComposerAidlTest
tests:
- SetActiveConfig/0_android_hardware_graphics_composer3_IComposer_default
- SetActiveConfigPowerCycle/0_android_hardware_graphics_composer3_IComposer_default

Change-Id: Id34619ea83accf3dfff645c202fdf2ca743e2bb6
Signed-off-by: Nicolas Belin <nbelin@baylibre.com>

default.xml

@@ -1417,7 +1417,7 @@
 
 <!-- AOSP -->
   <remove-project name="platform/external/drm_hwcomposer" />
-  <project path="external/drm_hwcomposer" name="platform/external/drm_hwcomposer" revision="2852f7d46de5d0109a828a13589f1eb518f1acd6" groups="drm_hwcomposer,pdk-fs" />
+  <project path="external/drm_hwcomposer" name="platform/external/drm_hwcomposer" revision="a8ef39578ca861e23160a0cd15df79bcf0e6d07b" groups="drm_hwcomposer,pdk-fs" />
 
 <!-- AOSP Forks -->
   <remove-project name="platform/external/v4l2_codec2" />