drm/i915: Don't assign to struct drm_device.pdev

Using struct drm_device.pdev is deprecated. Don't assign it. Users
should upcast from struct drm_device.dev.

v6:
	* also fix the assignment in selftests in this patch (Chris)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210429105101.25667-5-tzimmermann@suse.de

drivers/gpu/drm/i915/i915_drv.c

@@ -758,7 +758,6 @@ i915_driver_create(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (IS_ERR(i915))
 		return i915;
 
-	i915->drm.pdev = pdev;
 	pci_set_drvdata(pdev, i915);
 
 	/* Device parameters start as a copy of module parameters. */

drivers/gpu/drm/i915/selftests/mock_gem_device.c

@@ -146,7 +146,6 @@ struct drm_i915_private *mock_gem_device(void)
 	}
 
 	pci_set_drvdata(pdev, i915);
-	i915->drm.pdev = pdev;
 
 	dev_pm_domain_set(&pdev->dev, &pm_domain);
 	pm_runtime_enable(&pdev->dev);