staging: ozwpan: implement error handling in ozwpan_init()

Errors are correctly handled in oz_cdev_register() and oz_protocol_init(),
but then they are ignored in ozwpan_init().

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>