avr32: Convert BUG() to use unreachable()

Use the new unreachable() macro instead of for(;;);
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Acked-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/avr32/include/asm/bug.h

@@ -52,7 +52,7 @@
 #define BUG()								\
 	do {								\
 		_BUG_OR_WARN(0);					\
-		for (;;);						\
+		unreachable();						\
 	} while (0)
 
 #define WARN_ON(condition)							\