habanalabs: use get_task_pid() to take PID

The previous function we used, find_get_pid(), wasn't good in case
the user process was run inside docker.

As a result, we didn't had the PID and we couldn't kill the user
process in case the device got stuck and we needed to reset the
device.

Signed-off-by: Oded Gabbay <ogabbay@kernel.org>