nvme: Initialize the buffer before reading the contents
nvme: Initialize the buffer before reading the contents

Fixes a complaint from valgrind.

vathpela/fwupd,hughsie/fwupd,hughsie/fwupd,vathpela/fwupd,vathpela/fwupd,fwupd/fwupd,fwupd/fwupd,vathpela/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd