Update for cleanups in hwc interface

Also store the hwc_procs_t* into a dedicated field instead of one of
the hwc_composer_device_1_t::reserved_procs slots, which are supposed
to be NULL so the structure can be extended without breaking backwards
binary compatibility.

Change-Id: I11e6bc713958d854aba418242caa749cbcb21f1d
diff --git a/libhwcomposer/hwc_mdpcomp.cpp b/libhwcomposer/hwc_mdpcomp.cpp
index aa59cbd..7eaea7f 100644
--- a/libhwcomposer/hwc_mdpcomp.cpp
+++ b/libhwcomposer/hwc_mdpcomp.cpp
@@ -114,15 +114,13 @@
         return;
     }
 
-    hwc_procs* proc = (hwc_procs*)ctx->device.reserved_proc[0];
-
-    if(!proc) {
+    if(!ctx->proc) {
         ALOGE("%s: HWC proc not registered", __FUNCTION__);
         return;
     }
     sIdleFallBack = true;
     /* Trigger SF to redraw the current frame */
-    proc->invalidate(proc);
+    ctx->proc->invalidate(ctx->proc);
 }
 
 void MDPComp::reset(hwc_context_t *ctx, hwc_display_contents_1_t* list ) {