drm/i915/bios: Tolerate devdata==NULL in intel_bios_encoder_supports_dp_dual_mode()

If we have no VBT, or the VBT didn't declare the encoder
in question, we won't have the 'devdata' for the encoder.
Instead of oopsing just bail early.

We won't be able to tell whether the port is DP++ or not,
but so be it.

Cc: stable@vger.kernel.org
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10464
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240319092443.15769-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit 2641089)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

Author: vsyrjala

drivers/gpu/drm/i915/display/intel_bios.c

@@ -3382,6 +3382,9 @@ bool intel_bios_encoder_supports_dp_dual_mode(const struct intel_bios_encoder_da
 {
 	const struct child_device_config *child = &devdata->child;
 
+	if (!devdata)
+		return false;
+
 	if (!intel_bios_encoder_supports_dp(devdata) ||
 	    !intel_bios_encoder_supports_hdmi(devdata))
 		return false;