[libsycl] Fix build after olInit change (#182057)

After https://github.com/llvm/llvm-project/pull/181872 the function
takes an argument. Pass `nullptr` to have it do the same thing as
before.

This wasn't caught because the only builder that builds `libsycl` is not
in the production builder area at the moment.

Signed-off-by: Nick Sarnie <nick.sarnie@intel.com>

libsycl/src/detail/offload/offload_topology.cpp

@@ -56,7 +56,7 @@ void OffloadTopology::registerNewPlatformsAndDevices(
 }
 
 void discoverOffloadDevices() {
-  callAndThrow(olInit);
+  callAndThrow(olInit, nullptr);
 
   // liboffload returns devices sorted by backend + platform. We rely on this
   // behavior during device enumeration.