staging: solo6010: fix signess bug

video_nr is unsigned, so check video_nr >= 0 doesn't make sense.
The only "negative" value may be -1, so explicitly check for it.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>