drivers/isdn/hardware/icon: fix sparse warning: cast truncates bits

Fix this sparse warning:
  drivers/isdn/hardware/eicon/debug.c:1201:32: warning: cast truncates bits from constant value (1000 becomes 0)

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: David S. Miller <davem@davemloft.net>