ehci: update irq on reset

ehci: update irq on reset

After clearing the status register we also have to update the irq line
status.  Otherwise a irq which happends to be pending at reset time
causes a interrupt storm.  And the guest can't stop as the status
register doesn't indicate any pending interrupt.

Both NetBSD and FreeBSD hang on shutdown because of that.

Cc: qemu-stable@nongnu.org
Reported-by: Andrey Korolyov <andrey@xdel.ru>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1453203884-4125-1-git-send-email-kraxel@redhat.com
(cherry picked from commit 5a8660741a8aa19fbf8a5e8a2b3aac88664f4e66)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>