[OpenMP][libomptarget][Fix] Add missing array initialization (#76457)

Add missing array initialization as the array was not initialized and
the value zero was assumed.

GitOrigin-RevId: a01b58aef0e42fb1b52e358adf4c56678a884d37
diff --git a/libomptarget/test/offloading/struct_mapping_with_pointers.cpp b/libomptarget/test/offloading/struct_mapping_with_pointers.cpp
index befed12..f0fde50 100644
--- a/libomptarget/test/offloading/struct_mapping_with_pointers.cpp
+++ b/libomptarget/test/offloading/struct_mapping_with_pointers.cpp
@@ -29,6 +29,7 @@
 
   dat.datum[7] = 7;
   dat.more_datum[17] = 17;
+  dat.datum[dat.arr[0][0]] = 0;
 
   /// The struct is mapped with type 0x0 when the pointer fields are mapped.
   /// The struct is also map explicitely by the user. The second mapping by