systemcmds/tests: dataman test use proper signed type for dm_read() return

src/systemcmds/tests/test_dataman.c

@@ -98,7 +98,7 @@ task_main(int argc, char *argv[])
 		//PX4_INFO("ret: %d", ret);
 
 		if (ret != len) {
-			PX4_WARN("task %d: write failed, index %d, length %d", my_id, hash, len);
+			PX4_WARN("task %d: write failed (%d), index %d, length %d", my_id, ret, hash, len);
 			goto fail;
 		}
 
@@ -114,8 +114,8 @@ task_main(int argc, char *argv[])
 
 	for (unsigned i = 0; i < NUM_MISSIONS_TEST; i++) {
 		unsigned hash = i ^ my_id;
-		unsigned len2;
+		ssize_t len2;
-		unsigned len = (hash % (DM_MAX_DATA_SIZE / 2)) + 2;
+		ssize_t len = (hash % (DM_MAX_DATA_SIZE / 2)) + 2;
 
 		if ((len2 = dm_read(DM_KEY_WAYPOINTS_OFFBOARD_1, hash, buffer, sizeof(buffer))) < 2) {
 			PX4_WARN("task %d: read failed length test, index %d", my_id, hash);
@@ -126,7 +126,7 @@ task_main(int argc, char *argv[])
 			hit++;
 
 			if (len2 != len) {
-				PX4_WARN("task %d: read failed length test, index %d, wanted %d, got %d", my_id, hash, len, len2);
+				PX4_WARN("task %d: read failed length test, index %d, wanted %zu, got %zu", my_id, hash, len, len2);
 				goto fail;
 			}