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/drmcrtc.cpp b/drmcrtc.cpp
index c139869..1b354fe 100644
--- a/drmcrtc.cpp
+++ b/drmcrtc.cpp
@@ -31,12 +31,7 @@
       id_(c->crtc_id),
       pipe_(pipe),
       display_(-1),
-      x_(c->x),
-      y_(c->y),
-      width_(c->width),
-      height_(c->height),
-      mode_(&c->mode),
-      mode_valid_(c->mode_valid) {
+      mode_(&c->mode) {
 }
 
 int DrmCrtc::Init() {