AK: Unbreak building with extra debug macros

Author: https://github.com/BenWiederhake
Commit: 184b454e2f
Pull-request: https://github.com/SerenityOS/serenity/pull/3314

AK/MappedFile.cpp

@@ -57,7 +57,7 @@ MappedFile::MappedFile(const StringView& file_name)
     }
 
 #ifdef DEBUG_MAPPED_FILE
-    dbgprintf("MappedFile{%s} := { fd=%d, m_size=%u, m_map=%p }\n", file_name.characters(), fd, m_size, m_map);
+    dbgprintf("MappedFile{%s} := { fd=%d, m_size=%zu, m_map=%p }\n", file_name.to_string().characters(), fd, m_size, m_map);
 #endif
 
     close(fd);