trivial: Fix a tiny memory leak when writing DfuSe images
trivial: Fix a tiny memory leak when writing DfuSe images

Found using Coverity, many thanks.

vathpela/fwupd,fwupd/fwupd,superm1/fwupd,vathpela/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,superm1/fwupd,hughsie/fwupd,fwupd/fwupd,superm1/fwupd,fwupd/fwupd,hughsie/fwupd,vathpela/fwupd,vathpela/fwupd