alpha: Convert BUG() to use unreachable()

Use the new unreachable() macro instead of for(;;);

Signed-off-by: David Daney <[e-mail]>
CC: Richard Henderson <[e-mail]>
CC: Ivan Kokshaysky <[e-mail]>
CC: [e-mail]
Signed-off-by: Matt Turner <[e-mail]>

arch/alpha/include/asm/bug.h

···
 		"call_pal %0  # bugchk\n\t"				\
 		".long %1\n\t.8byte %2"					\
 		: : "i"(PAL_bugchk), "i"(__LINE__), "i"(__FILE__));	\
-	for ( ; ; ); } while (0)
+	unreachable();							\
+  } while (0)
 
 #define HAVE_ARCH_BUG
 #endif