dda_queue: optimize enqueue().

Suggestion by ItsDrone, see
http://forums.reprap.org/read.php?146,174364,174364#msg-174364

dda_queue.c

@@ -91,10 +91,6 @@ void queue_step() {
 /// add a move to the movebuffer
 /// \note this function waits for space to be available if necessary, check queue_full() first if waiting is a problem
 /// This is the only function that modifies mb_head and it always called from outside an interrupt.
-void enqueue(TARGET *t) {
-	enqueue_home(t, 0, 0);
-}
-
 void enqueue_home(TARGET *t, uint8_t endstop_check, uint8_t endstop_stop_cond) {
 	// don't call this function when the queue is full, but just in case, wait for a move to complete and free up the space for the passed target
 	while (queue_full())

dda_queue.h

@@ -28,9 +28,13 @@ void queue_step(void);
 
 // add a new target to the queue
 // t == NULL means add a wait for target temp to the queue
-void enqueue(TARGET *t);
 void enqueue_home(TARGET *t, uint8_t endstop_check, uint8_t endstop_stop_cond);
 
+static void enqueue(TARGET *) __attribute__ ((always_inline));
+inline void enqueue(TARGET *t) {
+  enqueue_home(t, 0, 0);
+}
+
 // called from step timer when current move is complete
 void next_move(void) __attribute__ ((hot));