Fix test action that tampered file at wrong offset

The implementation in writeZerosAtFileOffsetOnMicrodroid specifies the
offset of the output file by "skip" of "dd". But actually, "skip" is for
"if=", while "seek" is for "of=". The test expectation did not fail
coincidentally.

Bug: N/A
Test: testWriteFailedIfDetectsTampering
Change-Id: I89c9c96d250f4374e51a01c986aa1289b24ac236
diff --git a/authfs/tests/java/src/com/android/fs/AuthFsHostTest.java b/authfs/tests/java/src/com/android/fs/AuthFsHostTest.java
index 9a2e243..e7084ad 100644
--- a/authfs/tests/java/src/com/android/fs/AuthFsHostTest.java
+++ b/authfs/tests/java/src/com/android/fs/AuthFsHostTest.java
@@ -772,7 +772,7 @@
         String cmd = "dd if=/dev/zero of=" + filePath + " bs=1 count=" + numberOfZeros
                 + " conv=notrunc";
         if (offset > 0) {
-            cmd += " skip=" + offset;
+            cmd += " seek=" + offset;
         }
         if (writeThrough) {
             cmd += " direct";