fix(nodes/fpga): Fix cppcheck warning

Signed-off-by: Philipp Jungkamp <philipp.jungkamp@rwth-aachen.de>

Author: pjungkamp

lib/nodes/fpga.cpp

@@ -221,10 +221,10 @@ int FpgaNode::start() {
 // If fastWrite receives less signals than expected, the previous data
 // will be reused for the remaining signals
 int FpgaNode::fastWrite(Sample *smps[], unsigned cnt) {
-  Sample *smp = smps[0];
-
   assert(cnt == 1 && smps != nullptr && smps[0] != nullptr);
 
+  Sample *smp = smps[0];
+
   for (unsigned i = 0; i < smp->length; i++) {
     if (smp->signals->getByIndex(i)->type == SignalType::FLOAT) {
       (*accessorTxFloat)[i] = static_cast<float>(smp->data[i].f);