Fix issue like, rx_running is set 1 after first start rx.
But rx_running is still 1 after stop rx, which causes
dma can not be started when second start rx.
Change-Id: Id2f3a535da1b3609e8af287edbcc2e25fb7ae922
Signed-off-by: Huibin Hong <huibin.hong@rock-chips.com>