hwc: Use dynamic_fps node from /sys/devices/virtual/

- With SELinux, the HAL should write to sysfs nodes from
  "/sys/devices/virtual/graphics" instead of "/sys/class/graphics"
- Change HAL to use that file path.

Change-Id: I867a1f94c8f13afe5bbbcb5a61f93599938210d9
diff --git a/libhwcomposer/hwc_utils.cpp b/libhwcomposer/hwc_utils.cpp
index 4f3dbf0..adb3b9c 100644
--- a/libhwcomposer/hwc_utils.cpp
+++ b/libhwcomposer/hwc_utils.cpp
@@ -494,7 +494,7 @@
     const int fbNum = Overlay::getFbForDpy(dpy);
     char sysfsPath[qdutils::MAX_SYSFS_FILE_PATH];
     snprintf (sysfsPath, sizeof(sysfsPath),
-            "/sys/class/graphics/fb%d/dynamic_fps", fbNum);
+            "/sys/devices/virtual/graphics/fb%d/dynamic_fps", fbNum);
 
     int fd = open(sysfsPath, O_WRONLY);
     if(fd >= 0) {