staging: android: ion_test: fix check of platform_device_register_simple() error...

staging: android: ion_test: fix check of platform_device_register_simple() error code

commit ccbc2a9e7878ff09bcaed4893c2a2d3adbb797e2 upstream.

On error platform_device_register_simple() returns ERR_PTR() value,
check for NULL always fails. The change corrects the check itself and
propagates the returned error upwards.

Fixes: 81fb0b901397 ("staging: android: ion_test: unregister the platform device")
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>