Use indexing in preference to pointer arithmetic.

Change-Id: Ia90714e95af1e545f626bd5b6c99e40622e37286
diff --git a/src/fdt.c b/src/fdt.c
index 6383164..599fca4 100644
--- a/src/fdt.c
+++ b/src/fdt.c
@@ -50,7 +50,7 @@
 
 static void fdt_tokenizer_align(struct fdt_tokenizer *t)
 {
-	t->cur = (char *)(((size_t)t->cur + 3) & ~3);
+	t->cur = (char *)(((uintptr_t)t->cur + 3) & ~3);
 }
 
 static bool fdt_tokenizer_uint32(struct fdt_tokenizer *t, uint32_t *res)