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/clone.c b/cmd/clone.c
index 32473a0..a906207 100644
--- a/cmd/clone.c
+++ b/cmd/clone.c
@@ -34,7 +34,7 @@
 		printf("Unable to open destination device\n");
 		return 1;
 	}
-	requested = simple_strtoul(argv[5], &unit, 10);
+	requested = dectoul(argv[5], &unit);
 	srcbz = srcdesc->blksz;
 	destbz = destdesc->blksz;