dm: core: Fix devfdt_get_addr_ptr return value

According to the description of devfdt_get_addr_ptr, this function should
return NULL on failure, but currently it returns (void *)FDT_ADDR_T_NONE.

Fix this by making devfdt_get_addr_ptr return NULL on failure, as
described in the function comments. Also, update the drivers currently
checking (void *)FDT_ADDR_T_NONE to check for NULL.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/read.h b/include/dm/read.h
index cac7dd5..0a7aacd 100644
--- a/include/dm/read.h
+++ b/include/dm/read.h
@@ -802,9 +802,7 @@
 
 static inline void *dev_read_addr_ptr(const struct udevice *dev)
 {
-	void *addr = devfdt_get_addr_ptr(dev);
-
-	return ((fdt_addr_t)(uintptr_t)addr == FDT_ADDR_T_NONE) ? NULL : addr;
+	return devfdt_get_addr_ptr(dev);
 }
 
 static inline fdt_addr_t dev_read_addr_pci(const struct udevice *dev)