drm: bridge: dw_hdmi: switch to ->edid_read callback

Prefer using the struct drm_edid based callback and functions.

v2: Fix -Wuninitialized (kernel test robot)

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/400bfdeca4fd25b7624286e5969c4b0b1331c2b4.1706038510.git.jani.nikula@intel.com