uefi: Actually write the new device path if different than before
uefi: Actually write the new device path if different than before

If we add or remove a quirk from a machine using the uefi plugin then the new
setting is not used until the BootXXXX EFI key is manually removed. Rather than
just writing the contents of the found key back to the key (doh) just write the
new DP buffer contents if it is different from the previous buffer.

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