Fix an accidentally introduced formatting issue in zfs output.

Because the local 'index' variable shadows the index() function
it was replaced by 'i'.  Unfortunately when I made this change
I accidentally replaced one instance with 'j' resulting in the
short decimal values being printed incorrectly.

lib/libzfs/libzfs_util.c

@@ -551,7 +551,7 @@ zfs_nicenum(uint64_t num, char *buf, size_t buflen)
 		 */
 		for (j = 2; j >= 0; j--) {
 			if (snprintf(buf, buflen, "%.*f%c", j,
-			    (double)num / (1ULL << 10 * j), u) <= 5)
+			    (double)num / (1ULL << 10 * i), u) <= 5)
 				break;
 		}
 	}