mailbox: add sanity check for channel array

[ Upstream commit c1aad75 ]

Fail gracefully if there is no channel array attached to the mailbox
controller. Otherwise the later dereference will cause an OOPS which
might not be seen because mailbox controllers might instantiate very
early. Remove the comment explaining the obvious while here.

Fixes: 2b6d83e ("mailbox: Introduce framework for mailbox")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Wolfram Sang

drivers/mailbox/mailbox.c

@@ -520,8 +520,7 @@ int mbox_controller_register(struct mbox_controller *mbox)
 {
 	int i, txdone;
 
-	/* Sanity check */
-	if (!mbox || !mbox->dev || !mbox->ops || !mbox->num_chans)
+	if (!mbox || !mbox->dev || !mbox->ops || !mbox->chans || !mbox->num_chans)
 		return -EINVAL;
 
 	if (mbox->txdone_irq)