rockchip: video: rk3288_hdmi: Add missing call to dw_hdmi_enable()

The RK3288 HDMI driver's rk3288_hdmi_enable() currently lacks a call to
dw_hdmi_enable(). Thus, the HDMI output never gets enabled.

Signed-off-by: Niklas Schulze <me@jns.io>
Cc: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Kever Yang <Kever.yang@rock-chips.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>