mailbox: ti-msgmgr: Off by one in ti_msgmgr_of_xlate()

mailbox: ti-msgmgr: Off by one in ti_msgmgr_of_xlate()

The > comparison should be >= or we access one element beyond the end
of the array.

(The inst->qinsts[] array is allocated in the ti_msgmgr_probe() function
and it has ->num_valid_queues elements.)

Fixes: fcdad9a3b360 ("mailbox: ti-msgmgr: Add support for Secure Proxy")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>