drm/i915/dpio: Derive the phy from the port rather than pipe in encoder hooks

drm/i915/dpio: Derive the phy from the port rather than pipe in encoder hooks

In the encoder hooks we are dealing primarily with the encoder,
so derive the DPIO PHY from the encoder rather than the pipe.
Technically this doesn't matter as we can't cross connect
pipes<->port across PHY boundaries, but it does conveny the
intention more accurately.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240422083457.23815-10-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>