use sbrk(0) instead of end to get the uninitalized memory...

This is better, as if anyone allocated memory before, we will not use
that memory, and still use uninitalized memory..

strobe_rng_init.c

@@ -33,18 +33,14 @@
 
 #include <utilities.h>
 
+#include <unistd.h>
+
 #define nitems(x)	(sizeof(x) / sizeof *(x))
 #define DEFINE_RNG_SAVE	1
 #if DEFINE_RNG_SAVE
 const rng_word_t rng_save[roundup(32, sizeof(rng_word_t)) / sizeof(rng_word_t)] __attribute__ ((section (".eeprom")));
 #endif
 
-/*
- * Note: This is the end of allocated SRAM, aka, the begining of
- * uninitalized SRAM.
- */
-extern uint8_t end;
-
 void
 strobe_rng_init(void)
 {
@@ -58,8 +54,10 @@ strobe_rng_init(void)
 	/*
 	 * On first boot, SRAM is uninitialized and randomness from
 	 * it is used.
+	 *
+	 * Note: This depends upon sbrk pointing to uinitalized SRAM.
 	 */
-	strobe_seed_prng(&end, 2*1024);
+	strobe_seed_prng(sbrk(0), 2*1024);
 
 }