[media] lirc_zilog: Use sizeof(*p) instead of sizeof(struct P)

Fix all checkpatch reported issues for "CHECK: Prefer
kzalloc(sizeof(*<p>)...) over kzalloc(sizeof(struct <P>)...)".

Other similar case in the code already using recommended style, so make
it all consistent with the recommended practice.

Signed-off-by: Ricardo Silva <rjpdasilva@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>