global: Convert simple_strtoul() with decimal to dectoul()

It is a pain to have to specify the value 10 in each call. Add a new
dectoul() function and update the code to use it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/ufs.c b/cmd/ufs.c
index 858cd49..d4a1e66 100644
--- a/cmd/ufs.c
+++ b/cmd/ufs.c
@@ -16,7 +16,7 @@
 	if (argc >= 2) {
 		if (!strcmp(argv[1], "init")) {
 			if (argc == 3) {
-				dev = simple_strtoul(argv[2], NULL, 10);
+				dev = dectoul(argv[2], NULL);
 				ret = ufs_probe_dev(dev);
 				if (ret)
 					return CMD_RET_FAILURE;