ravb: clear RIC1 in init instead of stop

AVB-DMAC Receive FIFO Warning interrupt is not enabled, so it is not
necessary to disable the interrupt in ravb_close().
On the other hand, this patch disables the interrupt in ravb_dmac_init() to
prevent the possibility that the interrupt is issued by the state that
a boot loader left.

Signed-off-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>