drm/bridge: nxp-ptn3460: switch to ->edid_read callback

Prefer using the struct drm_edid based callback and functions.

v2: Fix -Wsometimes-uninitialized (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/6f4e48af3bf4d7782e8dfad703b6f22a69e94bf8.1706038510.git.jani.nikula@intel.com