ltq-tapi: Fix compile with kernel 5.15

ltq-tapi: Fix compile with kernel 5.15

Do not use find_vpid(), but get_task_pid() to get the pid from
pThrCntrl->tid. This is now a ponter to struct task_struct instead of
an integer.

This fixes the build of ltq-tapi with lantiq/xway.

Signed-off-by: Hauke Mehrtens <[email protected]>