of_irq_get_byname() may return 0 as well as negative error number on
failure, while the driver only checks for the negative values. The driver
would then call request_irq(0, ...) in ti_msgmgr_queue_startup() and never
get a valid channel interrupt.
Check for 'qinst->irq <= 0' instead and return -ENXIO from
ti_msgmgr_queue_setup() and this fail the driver's probe iff
of_irq_get_byname() returned 0.[...]
Fixes: aace66b170ce ("mailbox: Introduce TI message manager driver")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>