irda: use msecs_to_jiffies for conversions

This is only an API consolidation and should make things more readable
it replaces  var * HZ / 1000  constructs by  msecs_to_jiffies(var).

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: David S. Miller <davem@davemloft.net>