logd: fix bad test assumptions

SerializedLogChunk.three_logs assumes that log buffers are
zero-initialized, but they are not.  This causes test failures on
host.

Test: this test passes
Change-Id: I0dfa282bdc36eaa4e8e39d85c5227f717b45ec2a
diff --git a/logd/SerializedLogChunkTest.cpp b/logd/SerializedLogChunkTest.cpp
index 3b45125..862c3fe 100644
--- a/logd/SerializedLogChunkTest.cpp
+++ b/logd/SerializedLogChunkTest.cpp
@@ -99,13 +99,9 @@
             "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"                  // Timestamp
             "\x0C\x00last message";                             // msg_len + message
 
-    for (size_t i = 0; i < chunk_size; ++i) {
-        if (i < sizeof(expected_buffer_data)) {
-            EXPECT_EQ(static_cast<uint8_t>(expected_buffer_data[i]), chunk.data()[i])
-                    << "position: " << i;
-        } else {
-            EXPECT_EQ(0, chunk.data()[i]) << "position: " << i;
-        }
+    for (size_t i = 0; i < sizeof(expected_buffer_data); ++i) {
+        EXPECT_EQ(static_cast<uint8_t>(expected_buffer_data[i]), chunk.data()[i])
+                << "position: " << i;
     }
 }