net: dsa: microchip: Fix error path in PTP IRQ setup

In the Linux kernel, the following vulnerability has been resolved:

net: dsa: microchip: Fix error path in PTP IRQ setup

If request_threaded_irq() fails during the PTP message IRQ setup, the

newly created IRQ mapping is never disposed. Indeed, the

ksz_ptp_irq_setup()'s error path only frees the mappings that were

successfully set up.

Dispose the newly created mapping if the associated

request_threaded_irq() fails at setup.