svm: finish all queues in svm_pointer_passing (#2209)

The `svm_pointer_passing` test has unflushed buffer unmap commands
queued, which a runtime might process after the `clSVMFree` calls at the
end of the test (through implicit flushing when destroying the queues at
e.g. program exit handlers).

This is only an issue when running the test with multiple devices.

However I think this was caused by a simple typo given the `clFinish`
was simply in the wrong block.

test_conformance/SVM/test_pointer_passing.cpp

@@ -127,10 +127,10 @@ REGISTER_TEST(svm_pointer_passing)
                     return -1;
                 }
             }
-        }
 
-        error = clFinish(cmdq);
+            error = clFinish(cmdq);
-        test_error(error, "clFinish failed");
+            test_error(error, "clFinish failed");
+        }
     }