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 de30122bb58fee7b0f94bcfabab595b6ad757336 missed to remove this variable
too.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/arch/avr32/lib/board.c b/arch/avr32/lib/board.c
index b390a6c..d7a64b4 100644
--- a/arch/avr32/lib/board.c
+++ b/arch/avr32/lib/board.c
@@ -254,7 +254,6 @@
 #ifndef CONFIG_ENV_IS_NOWHERE
 	extern char * env_name_spec;
 #endif
-	char *s;
 	bd_t *bd;
 
 	gd = new_gd;