Doc: Fix QByteArray::toFloat snippet

Amends dc133765ec

Change-Id: I0550e94651dcf2434a7b57b7ae845a5b40cb5cc4
Reviewed-by: Martin Smith <martin.smith@qt.io>

src/corelib/doc/snippets/code/src_corelib_tools_qbytearray.cpp

@@ -363,7 +363,7 @@ a = str.toDouble(&ok);             // a == 0, ok == false
 //! [38float]
 QByteArray string("1234.56");
 bool ok;
-double a = string.toFloat(&ok);    // a == 1234.56, ok == true
+float a = string.toFloat(&ok);    // a == 1234.56, ok == true
 
 string = "1234.56 Volt";
 a = str.toFloat(&ok);              // a == 0, ok == false