membuff: Rename functions to have membuf_ prefix

The double 'f' is not necessary and is a bit annoying as elsewhere in
U-Boot we use 'buf'. Rename all the functions before it is used more
widely.

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 db76988..756fef6 100644
--- a/drivers/usb/emul/sandbox_keyb.c
+++ b/drivers/usb/emul/sandbox_keyb.c
@@ -167,7 +167,7 @@
 	struct sandbox_keyb_priv *priv = dev_get_priv(dev);
 	int ret;
 
-	ret = membuff_put(&priv->in, scancode, USB_KBD_BOOT_REPORT_SIZE);
+	ret = membuf_put(&priv->in, scancode, USB_KBD_BOOT_REPORT_SIZE);
 	if (ret != USB_KBD_BOOT_REPORT_SIZE)
 		return -ENOSPC;
 
@@ -194,7 +194,7 @@
 	if (length < USB_KBD_BOOT_REPORT_SIZE)
 		return 0;
 
-	membuff_get(&priv->in, buffer, USB_KBD_BOOT_REPORT_SIZE);
+	membuf_get(&priv->in, buffer, USB_KBD_BOOT_REPORT_SIZE);
 
 	return 0;
 }
@@ -220,7 +220,7 @@
 	struct sandbox_keyb_priv *priv = dev_get_priv(dev);
 
 	/* Provide an 80 character keyboard buffer */
-	return membuff_new(&priv->in, 80 * USB_KBD_BOOT_REPORT_SIZE);
+	return membuf_new(&priv->in, 80 * USB_KBD_BOOT_REPORT_SIZE);
 }
 
 static const struct dm_usb_ops sandbox_usb_keyb_ops = {