df: trivial 64-bit fix

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/coreutils/df.c b/coreutils/df.c
index 624ad94..a0e6fe0 100644
--- a/coreutils/df.c
+++ b/coreutils/df.c
@@ -183,7 +183,7 @@
 			if (dev_len > 20) {
 				printf("%s\n%20s", device, "");
 			} else {
-				printf("%s%*s", device, 20 - dev_len, "");
+				printf("%s%*s", device, 20 - (int)dev_len, "");
 			}
 #else
 			if (printf("\n%-20s" + 1, device) > 20)