drm/i915: Fix oops on platforms w/o hpd support

We don't have hpd support on i8xx/i915 which means hotplug_funcs==NULL.
Let's not oops when loading the driver on one those machines.

v2: Drop the redundant function pointer check (Jani)

Cc: Dave Airlie <airlied@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Fixes: cd030c7c ("drm/i915: constify hotplug function vtable.")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211014090941.12159-5-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -215,7 +215,7 @@ intel_hpd_irq_storm_switch_to_polling(struct drm_i915_private *dev_priv)
 
 static void intel_hpd_irq_setup(struct drm_i915_private *i915)
 {
-	if (i915->display_irqs_enabled && i915->hotplug_funcs->hpd_irq_setup)
+	if (i915->display_irqs_enabled && i915->hotplug_funcs)
 		i915->hotplug_funcs->hpd_irq_setup(i915);
 }