When the probe method of a driver fails, linux_pci_attach_device() only
dropped its reference on the device. Like on detach (see the previous
change), the devres actions are then not run if one of them holds a
reference on the device, which is what devm_drm_dev_alloc() does through the
drm_device. The device is never released, the drm_device is leaked with its
minor, its managed memory and its debugfs entries: unloading the driver
after a failed load (e.g. a missing firmware) printed
"WARNING !xa_empty(&drm_minors_xa)" and leaked memory.
Linux releases the devres resources of a device whose probe failed, so do the
same.