Fixed DMA time comparison.

Change-Id: I9aa454f3a3c75bd2ad65c0bcb62591e1acbc17f8
diff --git a/frc971/wpilib/dma_edge_counting.h b/frc971/wpilib/dma_edge_counting.h
index c145268..9347c83 100644
--- a/frc971/wpilib/dma_edge_counting.h
+++ b/frc971/wpilib/dma_edge_counting.h
@@ -165,7 +165,7 @@
   ::std::vector<DMASampleHandlerInterface *> handlers_;
 
   // The time at which we most recently read the sensor values.
-  double sample_time_ = 0.0;
+  uint32_t sample_time_ = 0.0;
 
   DISALLOW_COPY_AND_ASSIGN(DMASynchronizer);
 };