kern: default to release config

libraries/libmesosphere/include/mesosphere/kern_debug_log.hpp

@@ -40,7 +40,7 @@ namespace ams::kern {
 #ifndef MESOSPHERE_DEBUG_LOG_SELECTED
 
     #ifdef ATMOSPHERE_BOARD_NINTENDO_NX
-        #define MESOSPHERE_DEBUG_LOG_USE_UART_C
+        #define MESOSPHERE_DEBUG_LOG_USE_UART_A
     #else
         #error "Unknown board for Default Debug Log Source"
     #endif