staging: rtl8188eu: use msecs_to_jiffies for conversions

This is only an API consolidation to make things more readable.
Instances of  var * HZ / 1000  are replaced by  msecs_to_jiffies(var).

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