selftests: Use lirc.h from kernel tree, not from system

When the system lirc.h is older than v4.16, you will get errors like:

ir_loopback.c:32:16: error: field ‘proto’ has incomplete type
  enum rc_proto proto;

Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Shuah Khan <shuah@kernel.org>