Debugger: use QString::fromLatin1 instead of QString::fromAscii

By source - latin1 is really expected as there is no any check
or usage of QTextCodec::setCodecForCStrings() currently.

QString::fromAscii() might break 'Latin1' input in some cases.

A quote from documentation about QString::fromAscii():

"Note that, despite the name, this function actually uses the
codec defined by QTextCodec::setCodecForCStrings() to convert str
to Unicode. Depending on the codec, it may not accept valid
US-ASCII (ANSI X3.4-1986) input. If no codec has been set, this
function does the same as fromLatin1()."

Change-Id: I49cf047ca674d2ec621b517c635d1927bb2e796f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
Reviewed-by: hjk <qthjk@ovi.com>