The channel index is represented by an unsigned variable 'u32 chan'. We
don't need to check whether it is less than zero, the 'chan < 0' statement
is always false. Remove it.

Link: https://lore.kernel.org/r/1588162218-61757-1-git-send-email-wangxiongfeng2@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>