Change uses of {to,from}Ascii to {to,from}Latin1 [Linguist]

This operation should be a no-op anyway, since at this point in time,
the fromAscii and toAscii functions simply call their fromLatin1 and
toLatin1 counterparts.

Task-number: QTBUG-21872
Change-Id: Ibb3c04114e1a311ff70ef649d977524a6dfec0aa
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>