Fix constant type to match assigned variable type

Fix constant type to match assigned variable type

Some compilers assume a literal value is a certain byte-length without
checking the type to which it is being assigned, giving a compile-time
warning: a default of 'long' is a mismatch when assigning to a guint64
when the latter is a 'long long'. Use one of glib's standard macros to
specify the type of the constant to match the variable type.

https://bugzilla.gnome.org/show_bug.cgi?id=688829