ram: rk3399: Fix .set_rate_index() error handling

Functions pointed to by this op pointer can return non-zero values
indicating an error.  Ensure any error value is propagated back up the
call-chain.

Signed-off-by: Lee Jones <lee@kernel.org>
Tested-by: Xavier Drudis Ferran <xdrudis@tinet.cat>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
1 file changed