mailbox: Rename free() to rfree()

This function name conflicts with our desire to #define free() to
something else on sandbox. Since it deals with resources, rename it to
rfree().

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mailbox/tegra-hsp.c b/drivers/mailbox/tegra-hsp.c
index 9bee886..c463e6a 100644
--- a/drivers/mailbox/tegra-hsp.c
+++ b/drivers/mailbox/tegra-hsp.c
@@ -175,7 +175,7 @@
 struct mbox_ops tegra_hsp_mbox_ops = {
 	.of_xlate = tegra_hsp_of_xlate,
 	.request = tegra_hsp_request,
-	.free = tegra_hsp_free,
+	.rfree = tegra_hsp_free,
 	.send = tegra_hsp_send,
 	.recv = tegra_hsp_recv,
 };