drm/vc4: hdmi: Simplify exit path of vc4_hdmi_encoder_pre_crtc_configure

The exit path of vc4_hdmi_encoder_pre_crtc_configure() is fairly hard to
maintain given its numerous error conditions.

Switch to a goto based approach to simplify it.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>