sh: Fixup ndelay() xloops calculation for alternate HZ.

Currently the xloops calculation in ndelay() gets set to 0 when
calculated with HZ=250, fix up how we do the HZ factoring in order
to get this right for differing values.

Signed-off-by: kogiidena <kogiidena@eggplant.ddo.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>