arch/tile: fix pointer cast in cacheflush.c

Pragmatically it couldn't be wrong to cast pointers to long to compare
them (since all kernel addresses are in the top half of VA space),
but it's more correct to cast to unsigned long.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
diff --git a/arch/tile/lib/cacheflush.c b/arch/tile/lib/cacheflush.c
index 8928aac..6af2b97 100644
--- a/arch/tile/lib/cacheflush.c
+++ b/arch/tile/lib/cacheflush.c
@@ -109,7 +109,7 @@
 
 	/* Figure out how far back we need to go. */
 	base = p - (step_size * (load_count - 2));
-	if ((long)base < (long)buffer)
+	if ((unsigned long)base < (unsigned long)buffer)
 		base = buffer;
 
 	/*