libertas: don't retry commands

Retrying commands seldomly works, most often the firmware is in a
weird state anyway and needs the device to reset. So it's better
to report the broken state back to user-space.

Also rename command_timer_fn() into lbs_cmd_timeout_handler(),
which better reflect it's usage.

Signed-off-by: Holger Schurig <holgerschurig@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>