testing/radix-tree: fix a macro expansion bug

There are no parentheses around this macro and it causes a problem when
we do:

	index = rand() % THRASH_SIZE;

Link: http://lkml.kernel.org/r/20160715210953.GC19522@mwanda
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/radix-tree/tag_check.c

@@ -122,7 +122,7 @@ enum {
 	NODE_TAGGED = 2,
 };
 
-#define THRASH_SIZE		1000 * 1000
+#define THRASH_SIZE		(1000 * 1000)
 #define N 127
 #define BATCH	33