dda_queue.h: replace all tabs by spaces.

Another file 'clean' and only few changes, so likely not producing
a mess in future rebases. No functional changes.

dda_queue.h

@@ -1,21 +1,22 @@
-#ifndef	_DDA_QUEUE
-#define	_DDA_QUEUE
 
-#include	"dda.h"
-#include	"timer.h"
+#ifndef _DDA_QUEUE
+#define _DDA_QUEUE
+
+#include "dda.h"
+#include "timer.h"
 
 #define HEATER_WAIT_TIMEOUT 1000 MS
 
 /*
-	variables
+  variables
 */
 
 // this is the ringbuffer that holds the current and pending moves.
-extern uint8_t	mb_tail;
+extern uint8_t mb_tail;
 extern DDA movebuffer[MOVEBUFFER_SIZE];
 
 /*
-	methods
+  methods
 */
 
 // queue status methods
@@ -47,4 +48,4 @@ void queue_flush(void);
 // wait for queue to empty
 void queue_wait(void);
 
-#endif	/* _DDA_QUEUE */
+#endif /* _DDA_QUEUE */