There is no error number returned if loop driver fails in function
alloc_disk to add new loop device. Add a correct error number to make
user notify in this case.
Signed-off-by: NMinfei Huang <mnghuan@gmail.com>
Reviewed-by: NMing Lei <tom.leiming@gmail.com>
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>