I think the winner would depend on the situation, the time and place in which the fight occurs.
In the comic book series, when Zarathos, (the original Ghost Rider) had worshipers,
(check out the issue with the 'City of 10,000 Souls'😉
the more believed, the more powerful he became, theoretically in this way he has no limits.
Also it was mentioned very early in the series, that his flame could become solidified into any shape, more than simply a motorcycle.
When he had a large number of worshipers, instead of burning souls, he could consume them. So if Skeletor has a soul, it would be incinerated.
Finally, his original form was that of a huge animated stone figure.
Such was his power at one time, that he could even animate stone.
if Skeletor, who I admit is a powerful wizard, where to encounter The
Ghost Rider like this, I think Skeletor would have to summon all his supernatural allies in order to have a chance to win.
However Marvel dumbed down his power later, so that no mention of burning people was made any more and it was replaced by a simple 'stare'. Perhaps it was considered too controversial, because he also went from being a bona fide demon, to as Marvel now describes it,
'A magical being from a mystical dimension'
Demon is taboo I guess.
So it all depends which Ghost Rider takes on Skeletor.
The earlier Ghost Rider I think pretty much had the battle in the bag,
but the later, more politically correct Spirit of Vengeance would have his work cut out for him.