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

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

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: Icb3ab0e1f4f3173563f3de36115b5457cf1ba856
Reviewed-by: Mark Brand <mabrand@mabrand.nl>