dma: call rtio module to get time cursor position

More portable across RTIO implementations.

src/runtime/src/kernel/dma.rs

@@ -197,7 +197,7 @@ unsafe fn dma_record_output_prepare(timestamp: i64, target: i32,
 
 pub extern fn dma_record_output(target: i32, word: i32) {
     unsafe {
-        let timestamp = csr::rtio::now_read() as i64;
+        let timestamp = rtio::now_mu();
         let data = dma_record_output_prepare(timestamp, target, 1);
         data.copy_from_slice(&[
             (word >>  0) as u8,
@@ -212,7 +212,7 @@ pub extern fn dma_record_output_wide(target: i32, words: CSlice<i32>) {
     assert!(words.len() <= 16); // enforce the hardware limit
 
     unsafe {
-        let timestamp = csr::rtio::now_read() as i64;
+        let timestamp = rtio::now_mu();
         let mut data = dma_record_output_prepare(timestamp, target, words.len());
         for word in words.as_ref().iter() {
             data[..4].copy_from_slice(&[