Fix: v.u.d might be uninitialized

lttng-filter-interpreter.c:301:17: warning: ‘v.u.d’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   ptr->u.d = v.u.d;

Indeed it seems that the value is never fetched if we compare to other
call sites and the dynamic call site further below.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I542d6db7514a2c39afe3613228577f34f194d672