membuf: Rename struct

Rename the struct to match the function prefix and filenames.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/usb/emul/sandbox_keyb.c b/drivers/usb/emul/sandbox_keyb.c
index 756fef6..5ed8c2c 100644
--- a/drivers/usb/emul/sandbox_keyb.c
+++ b/drivers/usb/emul/sandbox_keyb.c
@@ -38,7 +38,7 @@
  *
  */
 struct sandbox_keyb_priv {
-	struct membuff in;
+	struct membuf in;
 };
 
 struct sandbox_keyb_plat {