vold: fix an offset one bug that makes partition 4 unusable

Change-Id: Ic8e18e6191ad7ee33162e36060b57a6802cf0883
diff --git a/DirectVolume.cpp b/DirectVolume.cpp
index 02c83d1..0d781d0 100644
--- a/DirectVolume.cpp
+++ b/DirectVolume.cpp
@@ -189,8 +189,8 @@
 #ifdef PARTITION_DEBUG
     SLOGD("Dv:partAdd: part_num = %d, minor = %d\n", part_num, minor);
 #endif
-    if (part_num >= MAX_PARTITIONS) {
-        SLOGE("Dv:partAdd: ignoring part_num = %d (max: %d)\n", part_num, MAX_PARTITIONS-1);
+    if (part_num > MAX_PARTITIONS) {
+        SLOGE("Dv:partAdd: ignoring part_num = %d (max: %d)\n", part_num, MAX_PARTITIONS);
     } else {
         mPartMinors[part_num -1] = minor;
     }