staging: rtl8712: cleanup of timeout conversions

This is only an API consolidation to make things more readable.
Instances of  var * HZ / 1000  are replaced by  msecs_to_jiffies(var).
As msecs_to_jiffies will return > 0 if it is passed a value > 0 the
== 0 check is not needed.

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>