rsi: remove redundant assignment

INVALID_QUEUE has been used as a return value,it is not necessary to
assign it to q_num,so just return INVALID_QUEUE.

Signed-off-by: wengjianfeng <wengjianfeng@yulong.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210203062717.1228-1-samirweng1979@163.com