drm_hwcomposer: fix warnings on unused variables and parameters

AOSP master now builds by default with -Werror, so fix all the warnings.
All the warnings are related to unused variables and parameters.

Reviewed-by: Robert Foss <robert.foss@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
diff --git a/platform.cpp b/platform.cpp
index e920872..56ab37e 100644
--- a/platform.cpp
+++ b/platform.cpp
@@ -142,8 +142,8 @@
 
 int PlanStagePrecomp::ProvisionPlanes(
     std::vector<DrmCompositionPlane> *composition,
-    std::map<size_t, DrmHwcLayer *> &layers, DrmCrtc *crtc,
-    std::vector<DrmPlane *> *planes) {
+    std::map<size_t, DrmHwcLayer *> &layers, DrmCrtc * /*crtc*/,
+    std::vector<DrmPlane *> * /*planes*/) {
   DrmCompositionPlane *precomp = GetPrecomp(composition);
   if (!precomp || precomp->source_layers().empty())
     return 0;