ptdma: pt_core_execute_cmd() should use spinlock

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

ptdma: pt_core_execute_cmd() should use spinlock

The interrupt handler (pt_core_irq_handler()) of the ptdma driver can be called from interrupt context. The code flow in this function can lead down to pt_core_execute_cmd() which will attempt to grab a mutex, which is not appropriate in interrupt context and ultimately leads to a kernel panic. The fix here changes this mutex to a spinlock, which has been verified to resolve the issue.