libertas: speeds up downloading of CF firmware

Keep the timeout the same (1000*500 == 100000 * 5), but take shorter
naps. Makes downloading the firmware slightly faster.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>