can't access external storage in ptp mode

In R, we can only access the primary storage in PTP mode.
However, we need to access the external storage in PTP mode sometimes
So, I made a change to let all storage accessible in both PTP and MTP mode

bug: 159769370

Change-Id: Id30516df802a165ccca99ddab7867d6ac3350339
diff --git a/src/com/android/mtp/MtpService.java b/src/com/android/mtp/MtpService.java
index 035c0f4..7301f4d 100644
--- a/src/com/android/mtp/MtpService.java
+++ b/src/com/android/mtp/MtpService.java
@@ -204,12 +204,8 @@
 
             // Add currently mounted and enabled storages to the server
             if (mUnlocked) {
-                if (mPtpMode) {
-                    addStorage(primary);
-                } else {
-                    for (StorageVolume v : mVolumeMap.values()) {
-                        addStorage(v);
-                    }
+                for (StorageVolume v : mVolumeMap.values()) {
+                    addStorage(v);
                 }
             }
             server.start();