smb/client: fix typo: GlobalMid_Sem -> GlobalMid_Lock

The comments have typos, fix that to not confuse readers.

Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>