[media] staging/lirc: fix mem leaks and ptr err usage

When the lirc drivers were converted over to using memdup_user, I
mistakenly also removed corresponding calls to kfree. Add those back. I
also screwed up on the allocation error check in lirc_serial, using if
(PTR_ERR()) instead of if (IS_ERR()), which broke transmit.

Reported-by: Jiri Fojtasek <jiri.fojtasek@hlohovec.net>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>