signal: check sig before setting info in kill_pid_usb_asyncio

signal: check sig before setting info in kill_pid_usb_asyncio

[ Upstream commit eaec2b0bd30690575c581eebffae64bfb7f684ac ]

In kill_pid_usb_asyncio, if signal is not valid, we do not need to
set info struct.

Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/f525fd08-1cf7-fb09-d20c-4359145eb940@huawei.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>