[media] rc: ir-lirc-codec: fix potential integer overflow

'n' may be bigger than MAX_INT*sizeof(int), if so checking of truncated
(int)(n/sizeof(int)) for LIRCBUF_SIZE overflow and then using nontruncated 'count'
doesn't make sense.  Also n may be up to sizeof(int)-1 bytes bigger than expected,
so check value of (n % sizeof(int)) too.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>