atm: he: use mdelay instead of large udelay constants

ARM cannot handle udelay for more than 2 miliseconds, and
it is rather bad style to block the cpu for 16ms anyway,
so let's use msleep instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Chas Williams <chas@cmf.nrl.navy.mil>
Cc: linux-atm-general@lists.sourceforge.net
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>