drm_hwcomposer: platformgeneric: Fix build

Propagate correct include path for gralloc_handle.h

Signed-off-by: Andrii Chepurnyi <andrii_chepurnyi@epam.com>
diff --git a/Android.mk b/Android.mk
index d5ee200..a14ad0a 100644
--- a/Android.mk
+++ b/Android.mk
@@ -99,6 +99,7 @@
 LOCAL_C_INCLUDES += external/minigbm/cros_gralloc/
 else
 LOCAL_CPPFLAGS += -DUSE_DRM_GENERIC_IMPORTER
+LOCAL_C_INCLUDES += external/libdrm/android/
 endif
 
 LOCAL_MODULE := hwcomposer.drm