[core]Coverity fix of dead code in (pr)elu reference implementation (#28407)

### Details:
- Fix Coverity issue in reference implementation of `ELU`, `PReLU`
operators of dead code for unsigned types.

### Tickets:
 - N/A

Signed-off-by: Raasz, Pawel <[email protected]>

Author: praasz

src/core/reference/include/openvino/reference/elu.hpp

@@ -7,13 +7,17 @@
 #include <cmath>
 #include <cstddef>
 
-namespace ov {
-namespace reference {
+#include "openvino/reference/copy.hpp"
+
+namespace ov::reference {
 template <typename T>
 void elu(const T* arg, T* out, size_t count, double alpha) {
-    for (size_t i = 0; i < count; i++) {
-        out[i] = arg[i] < T(0) ? T(alpha * (std::exp(arg[i]) - 1.0)) : arg[i];
+    if constexpr (std::is_unsigned_v<T>) {
+        copy(arg, out, count);
+    } else {
+        for (size_t i = 0; i < count; i++) {
+            out[i] = arg[i] < T(0) ? T(alpha * (std::exp(arg[i]) - 1.0)) : arg[i];
+        }
     }
 }
-}  // namespace reference
-}  // namespace ov
+}  // namespace ov::reference

src/core/reference/include/openvino/reference/prelu.hpp

@@ -11,13 +11,16 @@
 #include "openvino/op/util/attr_types.hpp"
 #include "openvino/reference/autobroadcast_binop.hpp"
 
-namespace ov {
-namespace reference {
+namespace ov::reference {
 namespace func {
 // Usage of custom function instead of lambda, gives smaller binary size.
 template <class T>
 T prelu(const T x, const T y) {
-    return x < T(0) ? x * y : x;
+    if constexpr (std::is_unsigned_v<T>) {
+        return x;
+    } else {
+        return x < T(0) ? x * y : x;
+    }
 }
 }  // namespace func
 
@@ -32,5 +35,4 @@ void prelu(const T* arg, const T* slope, T* out, const Shape& arg_shape, const S
     }
     autobroadcast_binop(arg, slope, out, arg_shape, slope_shape_tmp, op::AutoBroadcastType::NUMPY, func::prelu<T>);
 }
-}  // namespace reference
-}  // namespace ov
+}  // namespace ov::reference