Reduce the size of the ma_device_op_queue struct.

This in turn reduces the size of the `ma_device` struct by about half
a kilobyte or so.

miniaudio.h

@@ -7450,6 +7450,9 @@ typedef struct ma_device_op
 /*
 The device op queue is just a simple list with a mutex for the time being while I get everything set up. Might make
 this more efficient later.
+
+The capacity of this queue is tiny. In practice it's rare that there would be more than one item in the queue because
+typically a init/uninit/start/stop will typically be done in an orderly and synchronous manner.
 */
 typedef struct ma_device_op_queue
 {
@@ -7459,7 +7462,7 @@ typedef struct ma_device_op_queue
 #endif
     ma_uint32 count;
     ma_uint32 tail;
-    ma_device_op pItems[16];
+    ma_device_op pItems[4]; /* In practice, a capacity of 4 should be more than enough. */
 } ma_device_op_queue;