usblp: continuously poll for status

The usblp in 2.6.18 polled for status regardless if we actually needed it.
At some point I dropped it, to save the batteries if nothing else.
As it turned out, printers exist (e.g. Canon BJC-3000) that need prodding
this way or else they stop. This patch restores the old behaviour.
If you want to save battery, don't leave jobs in the print queue.

I tested this on my printers by printing and examining usbmon traces
to make sure status is being requested and printers continue to print.
Tuomas Jäntti verified the fix on BJC-3000.

Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>