libertas: struct lbs_private is declared duplicately

struct lbs_private has been declared at 22nd line.
Remove the duplicate.

Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210325064154.854245-1-wanjiabing@vivo.com