Fix handling naming at root of bemrc

[Vittly]

This works:

{
  levels: [
    { layer: 'desktop', naming: 'react' },
    { layer: 'common', naming: 'react' }
  ]
}

This does not:

{
  naming: 'react',
  levels: [
    { layer: 'desktop' },
    { layer: 'common' }
  ]
}

[Vittly]

Also does not work:

{
  levels: [
    { layer: 'common', naming: { /* naming-object */ } }
  ]
}

Because of this code. Need write something like

typeof object === 'string' ? presets[naming] : naming