drm/imx: dw_hdmi-imx: add end of array element to current control array

The loop iterating over curr_ctrl in dw_hdmi terminates on mpixelclock == ~0UL,
so there needs to be an end of list element here in case a mode with a pixel
clock larger than 216 MHz is set.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>