[SYCL] Fix return type of initialization value extraction (#16224)

This commit fixes an issue where the function extracting the initial
value of a device_global would return it as a reference to a different
type, which in turn could cause some unexpected behavior.

Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>

Author: steffenlarsen

sycl/include/sycl/ext/oneapi/device_global/device_global.hpp

@@ -83,7 +83,7 @@ class device_global_base {
 
 #ifndef __SYCL_DEVICE_ONLY__
   template <typename OtherT, typename OtherProps>
-  static constexpr const T &
+  static constexpr const OtherT &
   ExtractInitialVal(const device_global_base<OtherT, OtherProps> &Other) {
     if constexpr (OtherProps::template has_property<device_image_scope_key>())
       return Other.val;