efifb: Check efifb_pci_dev before using it

On some platforms like Hyper-V and RPi4 with UEFI firmware, efifb is not
a PCI device.

So make sure efifb_pci_dev is found before using it.

Fixes: a6c0fd3d5a8b ("efifb: Ensure graphics device for efifb stays at PCI D0")
BugLink: https://bugs.launchpad.net/bugs/1922403
Signed-off-by: Kai-Heng Feng <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
Reviewed-by: Alex Deucher <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/video/fbdev/efifb.c

···
 		goto err_fb_dealoc;
 	}
 	fb_info(info, "%s frame buffer device\n", info->fix.id);
-	pm_runtime_get_sync(&efifb_pci_dev->dev);
+	if (efifb_pci_dev)
+		pm_runtime_get_sync(&efifb_pci_dev->dev);
 	return 0;
 
 err_fb_dealoc:
···
 	unregister_framebuffer(info);
 	sysfs_remove_groups(&pdev->dev.kobj, efifb_groups);
 	framebuffer_release(info);
-	pm_runtime_put(&efifb_pci_dev->dev);
+	if (efifb_pci_dev)
+		pm_runtime_put(&efifb_pci_dev->dev);
 
 	return 0;
 }