efi_loader: fix memory freeing in efi_get_dp_from_boot()

efi_loader: fix memory freeing in efi_get_dp_from_boot()

efi_get_var() allocates memory which must be freed after the variable is
used. Since the device path is duplicated after we deserialize the load
options free the memory used for the variable payload

Fixes: db61e70e0d2a efi_loader: efi_dp_from_lo() should skip VenMedia node
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinric Schuchardt <heinrich.schuchardt@canonical.com>