Fix compiler warning sketch/Marlin_main.cpp:1846:1: warning: control reaches end of non-void function [-Wreturn-type].

Firmware/Marlin_main.cpp

@@ -1778,7 +1778,7 @@ void trace();
 char chunk[CHUNK_SIZE+SAFETY_MARGIN];
 int chunkHead = 0;
 
-int serial_read_stream() {
+void serial_read_stream() {
 
     setTargetHotend(0, 0);
     setTargetBed(0);
@@ -1839,9 +1839,7 @@ int serial_read_stream() {
             card.closefile();
             prusa_sd_card_upload = false;
             SERIAL_PROTOCOLLNRPGM(MSG_FILE_SAVED);
-            return 0;
         }
-
     }
 }