make powerpc BUG_ON() OK with pointers and bitwise

Since powerpc insists on printing the _value_ of condition
and on casting it to long...  At least let's make it a force-cast.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-powerpc/bug.h

@@ -79,7 +79,7 @@
 		_EMIT_BUG_ENTRY					\
 		: : "i" (__FILE__), "i" (__LINE__), "i" (0),	\
 		  "i" (sizeof(struct bug_entry)),		\
-		  "r" ((long)(x)));				\
+		  "r" ((__force long)(x)));			\
 	}							\
 } while (0)