staging: pi433: fix error return code in pi433_probe()

Fix to return negative error code -ENOMEM from cdev alloc failed error
handling case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20200428150650.102340-1-weiyongjun1@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>