log: Move "Pre-allocating up to position 0x[...] in [...].dat" log message to debug category

src/flatfile.cpp

@@ -66,7 +66,7 @@ size_t FlatFileSeq::Allocate(const FlatFilePos& pos, size_t add_size, bool& out_
         if (CheckDiskSpace(m_dir, inc_size)) {
             FILE *file = Open(pos);
             if (file) {
-                LogPrintf("Pre-allocating up to position 0x%x in %s%05u.dat\n", new_size, m_prefix, pos.nFile);
+                LogPrint(BCLog::VALIDATION, "Pre-allocating up to position 0x%x in %s%05u.dat\n", new_size, m_prefix, pos.nFile);
                 AllocateFileRange(file, pos.nPos, inc_size);
                 fclose(file);
                 return inc_size;