doc: driver-model: there is no UCLASS_SATA

%s/UCLASS_SATA/UCLASS_AHCI/g

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/driver-model/design.rst b/doc/driver-model/design.rst
index 635effc..9e92727 100644
--- a/doc/driver-model/design.rst
+++ b/doc/driver-model/design.rst
@@ -613,7 +613,7 @@
    xhci_usb (UCLASS_USB)
       flash (UCLASS_FLASH_STORAGE)  - parent data/methods defined by USB bus
 
-   sata (UCLASS_SATA)
+   sata (UCLASS_AHCI)
       flash (UCLASS_FLASH_STORAGE)  - parent data/methods defined by SATA bus
 
    flash (UCLASS_FLASH_STORAGE)  - no parent data/methods (not on a bus)