clk: rockchip: rk3568: Fix clk selection in rk3568_pwm_get_clk

Fix use of wrong clk selection for CLK_PWM1 on RK3568.

Fixes: 4a262feb ("rockchip: rk3568: add clock driver")
Signed-off-by: Damon Ding <damon.ding@rock-chips.com>
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>