doc: usage: cmd: ums: fix dependencies

Replace CONFIG_USB_USB_GADGET by CONFIG_USB_GADGET_DOWNLOAD.

Signed-off-by: Thomas Perrot <thomas.perrot@bootlin.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/usage/cmd/ums.rst b/doc/usage/cmd/ums.rst
index 9d379e3..e962227 100644
--- a/doc/usage/cmd/ums.rst
+++ b/doc/usage/cmd/ums.rst
@@ -48,7 +48,7 @@
 -------------
 
 The ums command is only available if CONFIG_CMD_USB_MASS_STORAGE=y
-and depends on CONFIG_USB_USB_GADGET and CONFIG_BLK.
+which depends on CONFIG_USB_GADGET_DOWNLOAD and CONFIG_BLK.
 
 Return value
 ------------