Flesh out the UDDF xml parsing a bit more

Commit 28aba5a2062c ("Flesh out the UDDF xml parsing a bit more")
improved on parsing UDDF files by teaching "percent()" to also handle
pure fractions like UDDF uses. So in a UDDF file, an o2 value of "1.0"
means "100%".

But it turns out that I have a few dives with "1% He", and the "Turn
fractions into percent" logic also turns that into 100%.

So this makes the 'percent()' function a bit smarter. If it actually
finds a percentage-sign after the number, it knows it is already
percent, not a fraction. That disambiguates the two cases: "1.0" is
100%, but "1.0%" (note the explicit percentage sign) is 1%.

So now our native format cannot get confused, because it generally
tries to avoid naked numbers. Good choice.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>