rpi: Update the Raspberry Pi doucmentation URL

The Raspberry Pi Foundation has updated their documentation so update
the URL to the latest place to find the HW device revision codes.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index 55afaa5..e7bcee3 100644
--- a/board/raspberrypi/rpi/rpi.c
+++ b/board/raspberrypi/rpi/rpi.c
@@ -72,7 +72,7 @@
 #endif
 
 /*
- * https://www.raspberrypi.org/documentation/hardware/raspberrypi/revision-codes/README.md
+ * https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#raspberry-pi-revision-codes
  */
 struct rpi_model {
 	const char *name;