net: wwan: t7xx: Fix return type of t7xx_dl_add_timedout()

t7xx_dl_add_timedout() now return int 'ret', but the return type
is bool. Change the return type to int for furthor errcode upstream.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>