s390/tape: fix timer initialization in tape_std_assign()

s390/tape: fix timer initialization in tape_std_assign()

commit 9c6c273aa424 ("timer: Remove init_timer_on_stack() in favor
of timer_setup_on_stack()") changed the timer setup from
init_timer_on_stack(() to timer_setup(), but missed to change the
mod_timer() call. And while at it, use msecs_to_jiffies() instead
of the open coded timeout calculation.

Cc: stable@vger.kernel.org
Fixes: 9c6c273aa424 ("timer: Remove init_timer_on_stack() in favor of timer_setup_on_stack()")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>