umem: fix error return code in mm_pci_probe()

Fix to return negative error code -ENOMEM from the blk_alloc_queue()
and dma_alloc_coherent() error handling cases instead of 0, as done
elsewhere in this function.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210308123501.2573816-1-weiyongjun1@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>