eta overflow fix

Sometime I get eta's like "eta 4294967286m:4294967266s" , just an overflow
issue. The following patch fixes the issue.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/eta.c b/eta.c
index 5b8a687..766f650 100644
--- a/eta.c
+++ b/eta.c
@@ -66,7 +66,7 @@
 /*
  * Convert seconds to a printable string.
  */
-static void eta_to_str(char *str, int eta_sec)
+static void eta_to_str(char *str, unsigned long eta_sec)
 {
 	unsigned int d, h, m, s;
 	int disp_hour = 0;