cpu/nrf51822: adjusted default stack sizes

cpu/nrf51822/include/cpu-conf.h

@@ -22,17 +22,14 @@
 #include "nrf51.h"
 #include "nrf51_bitfields.h"
 
-
 /**
  * @name Kernel configuration
- *
- * TODO: measure and adjust for the cortex-m0
  * @{
  */
-#define KERNEL_CONF_STACKSIZE_PRINTF    (524)
+#define KERNEL_CONF_STACKSIZE_PRINTF    (512)
 
 #ifndef KERNEL_CONF_STACKSIZE_DEFAULT
-#define KERNEL_CONF_STACKSIZE_DEFAULT   (524)
+#define KERNEL_CONF_STACKSIZE_DEFAULT   (512)
 #endif
 
 #define KERNEL_CONF_STACKSIZE_IDLE      (256)