t/Makefile: don't define TEST_RESULTS_DIRECTORY recursively

Commit 54bb901 (t/Makefile: fix result handling with
TEST_OUTPUT_DIRECTORY - 2013-04-26) incorrectly defined
TEST_RESULTS_DIRECTORY relative to itself, when it should be relative to
TEST_OUTPUT_DIRECTORY.  Fix this.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/Makefile

@@ -16,7 +16,7 @@ DEFAULT_TEST_TARGET ?= test
 TEST_LINT ?= test-lint-duplicates test-lint-executable
 
 ifdef TEST_OUTPUT_DIRECTORY
-TEST_RESULTS_DIRECTORY = $(TEST_RESULTS_DIRECTORY)/test-results
+TEST_RESULTS_DIRECTORY = $(TEST_OUTPUT_DIRECTORY)/test-results
 else
 TEST_RESULTS_DIRECTORY = test-results
 endif