Update path for seting USB mass storage backing store

Change-Id: I0e5fab1624e5ef5d2f55e2584d8adc1b6bab91b0
Signed-off-by: Mike Lockwood <lockwood@android.com>
diff --git a/VolumeManager.cpp b/VolumeManager.cpp
index c41baf3..88ac07c 100644
--- a/VolumeManager.cpp
+++ b/VolumeManager.cpp
@@ -43,6 +43,8 @@
 #include "Asec.h"
 #include "cryptfs.h"
 
+#define MASS_STORAGE_FILE_PATH  "/sys/class/android_usb/android0/f_mass_storage/lun/file"
+
 VolumeManager *VolumeManager::sInstance = NULL;
 
 VolumeManager *VolumeManager::Instance() {
@@ -937,8 +939,7 @@
              sizeof(nodepath), "/dev/block/vold/%d:%d",
              MAJOR(d), MINOR(d));
 
-    if ((fd = open("/sys/devices/platform/usb_mass_storage/lun0/file",
-                   O_WRONLY)) < 0) {
+    if ((fd = open(MASS_STORAGE_FILE_PATH, O_WRONLY)) < 0) {
         SLOGE("Unable to open ums lunfile (%s)", strerror(errno));
         return -1;
     }
@@ -988,7 +989,7 @@
     }
 
     int fd;
-    if ((fd = open("/sys/devices/platform/usb_mass_storage/lun0/file", O_WRONLY)) < 0) {
+    if ((fd = open(MASS_STORAGE_FILE_PATH, O_WRONLY)) < 0) {
         SLOGE("Unable to open ums lunfile (%s)", strerror(errno));
         return -1;
     }