spl: Drop use of uintptr_t

U-Boot uses ulong for addresses. It is confusing to use uintptr_t in a
few places, since it makes people wonder if the types are compatible.
Change the few occurences in SPL to use ulong

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_fit.c b/common/spl/spl_fit.c
index 3160f57..ef40a50 100644
--- a/common/spl/spl_fit.c
+++ b/common/spl/spl_fit.c
@@ -862,7 +862,7 @@
 {
 	struct bootm_headers images;
 	const char *fit_uname_config = NULL;
-	uintptr_t fdt_hack;
+	ulong fdt_hack;
 	const char *uname;
 	ulong fw_data = 0, dt_data = 0, img_data = 0;
 	ulong fw_len = 0, dt_len = 0, img_len = 0;