s390: convert to msecs_to_jiffies()

Instead of using the old 'jiffies + HZ {/,*} something' calculation
use msecs_to_jiffies() as that makes the code more readable.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>