libobs/util: Rename da_swap_item to da_swap

The name was inconsistent with the darray_swap function that it's a
macro for.

libobs/util/darray.h

@@ -521,7 +521,7 @@ static inline void darray_swap(const size_t element_size,
 #define da_move_item(v, from, to) \
 	darray_move_item(sizeof(*v.array), &v.da, from, to)
 
-#define da_swap_item(v, idx1, idx2) \
+#define da_swap(v, idx1, idx2) \
 	darray_swap(sizeof(v.array), &v.da, idx1, idx2)
 
 #ifdef __cplusplus