avr32:board.c: fix compile warning

This patch fixes following warning:

---8<---
board.c: In function 'board_init_r':
board.c:257: warning: unused variable 's'
--->8---

Patch de30122b missed to remove this variable
too.
Signed-off-by: NAndreas Bießmann <andreas.devel@googlemail.com>

arch/avr32/lib/board.c

@@ -254,7 +254,6 @@ void board_init_r(gd_t *new_gd, ulong dest_addr)
 #ifndef CONFIG_ENV_IS_NOWHERE
 	extern char * env_name_spec;
 #endif
-	char *s;
 	bd_t *bd;
 
 	gd = new_gd;