efi_generate_file_device_path(): fix one error case's free path.
efi_generate_file_device_path(): fix one error case's free path.

When efi_generate_file_device_path() gets an error from
find_parent_devpath(), it currently just returns an error, rather than
freeing up its intermediate resources.  So free them.

Found by covscan.

Signed-off-by: Peter Jones <2e0a021e603479ff81838c00c3b770daca4e0214@redhat.com>

rhinstaller/efivar,rhboot/efivar,rhboot/efivar,vathpela/efivar-devel,rhinstaller/efivar