Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/motors/peripheral/adc_dma.cc b/motors/peripheral/adc_dma.cc
index 15d50eb..11cdbb6 100644
--- a/motors/peripheral/adc_dma.cc
+++ b/motors/peripheral/adc_dma.cc
@@ -52,8 +52,7 @@
 //   8. Read ADC0.RB and ADC1.RB
 //   9. Go back to step #3
 
-namespace frc971 {
-namespace teensy {
+namespace frc971::teensy {
 namespace {
 
 constexpr uint32_t pdb_sc(int pdb_input) {
@@ -275,5 +274,4 @@
                 V_PDB_EN(3) /* Enable our two */;
 }
 
-}  // namespace teensy
-}  // namespace frc971
+}  // namespace frc971::teensy