mailbox: sprd: clear delivery flag before handling TX done

mailbox: sprd: clear delivery flag before handling TX done

[ Upstream commit c77661d60d4223bf2ff10d409beb0c3b2021183b ]

If there are any pending messages in the mailbox queue, they are sent
as soon as a TX done event arrives from the driver. This may trigger a
new delivery interrupt while the previous one is still being handled.
If the delivery status is cleared after this, the interrupt is lost.
To prevent this from happening, clear the delivery status immediately
after checking it and before any new messages are sent.

Signed-off-by: Otto Pflüger <otto.pflueger@abscue.de>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>