Fix the 404 nav bar to use the site configurable logo

[alex-bezek]

#103

I'm new to hugo, but from reading https://gohugo.io/variables/site/ it seems the . in a partial is the current context.
The main site navbar.html partial seems to work because the whole site is passed as context https://github.com/hossainemruz/toha/blob/master/layouts/index.html#L26 . However, the 404 nav bar partial doesn't seem to work because a dictionary partial is passed in https://github.com/hossainemruz/toha/blob/master/layouts/404.html#L6

Changing to use the global site function appears to fix it. Alternatively i could pass in either the full site object as context or add the .Site.Params.logo as a dictionary item to https://github.com/hossainemruz/toha/blob/master/layouts/404.html#L6

I've consumed this branch in my site to test

alex-bezek/blog#44
https://percy.io/alex-bezek/blog/builds/7343218
https://blog-git-demo-404-logo.alex-bezek.vercel.app/404.html

[hossainemruz]

Thank you @alex-bezek . Looks good.