comedi: jr3_pci: Fix synchronous deletion of timer

comedi: jr3_pci: Fix synchronous deletion of timer

When `jr3_pci_detach()` is called during device removal, it calls
`timer_delete_sync()` to stop the timer, but the timer expiry function
always reschedules the timer, so the synchronization is ineffective.

Call `timer_shutdown_sync()` instead.  It does not matter that the timer
expiry function pointer is cleared, because the device is being removed.

Fixes: 07b509e6584a5 ("Staging: comedi: add jr3_pci driver")
Cc: stable <stable@kernel.org>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20250415123901.13483-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>