Fix more signed-unsigned comparisons

Summary: Some comparisons left in log_test.cc and db_test.cc complained by make

Test Plan: make

Reviewers: dhruba, sheki

Reviewed By: dhruba

Differential Revision: https://reviews.facebook.net/D9537

db/db_test.cc

@@ -1480,7 +1480,7 @@ TEST(DBTest, CompactionFilter) {
   while (iter->Valid()) {
     ParsedInternalKey ikey;
     ASSERT_EQ(ParseInternalKey(iter->key(), &ikey), true);
-    ASSERT_NE(ikey.sequence, 0);
+    ASSERT_NE(ikey.sequence, (unsigned)0);
     count++;
     iter->Next();
   }

db/log_test.cc

@@ -450,13 +450,13 @@ TEST(LogTest, ErrorJoinsRecords) {
   Write("correct");
 
   // Wipe the middle block
-  for (int offset = kBlockSize; offset < 2*kBlockSize; offset++) {
+  for (unsigned int offset = kBlockSize; offset < 2*kBlockSize; offset++) {
     SetByte(offset, 'x');
   }
 
   ASSERT_EQ("correct", Read());
   ASSERT_EQ("EOF", Read());
-  const int dropped = DroppedBytes();
+  const unsigned int dropped = DroppedBytes();
   ASSERT_LE(dropped, 2*kBlockSize + 100);
   ASSERT_GE(dropped, 2*kBlockSize);
 }