nvme-pci: fix freeing of the HMB descriptor table

In the Linux kernel, the following vulnerability has been resolved:

nvme-pci: fix freeing of the HMB descriptor table

The HMB descriptor table is sized to the maximum number of descriptors

that could be used for a given device, but __nvme_alloc_host_mem could

break out of the loop earlier on memory allocation failure and end up

using less descriptors than planned for, which leads to an incorrect

size passed to dma_free_coherent.

In practice this was not showing up because the number of descriptors

tends to be low and the dma coherent allocator always allocates and

frees at least a page.