bpf_dbg: fix wrong register usage

The AND instruction is erroneously using the X register instead
of the K register.

Signed-off-by: Brendan Hickey <bhickey@google.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>