[SYCL][NFC] Fix "unused variable" warning (#886)

Signed-off-by: Alexey Bader <[email protected]>

Author: bader

sycl/source/detail/pi.cpp

@@ -84,6 +84,7 @@ bool bindPlugin(void *Library) {
   // TODO: Compare Supported versions and check for backward compatibility.
   // Make sure err is PI_SUCCESS.
   assert((err == PI_SUCCESS) && "Unexpected error when binding to Plugin.");
+  (void)err;
 
   // TODO: Return a more meaningful value/enum.
   return true;