Following condition which will cause NULL pointer dereference will
occur in nvme_free_host_mem() when it tries to remove pci device via
nvme_remove() especially after a failure of host memory allocation for HMB.
"(host_mem_descs == NULL) && (nr_host_mem_descs != 0)"
It's because __nr_host_mem_descs__ is not cleared to 0 unlike
__host_mem_descs__ is so.
Signed-off-by: Minwoo Im <email@example.com>
Signed-off-by: Christoph Hellwig <firstname.lastname@example.org>