selftests: futex: fix run_tests target

make -C tools/testing/selftests/futex/ run_tests doesn't run the futex
tests.

Running the tests when `dirname $(OUTPUT)` == $(PWD) doesn't work when
the $(OUTPUT) is $(PWD) which is the case when the test is run using
make -C tools/testing/selftests/futex/ run_tests.

Fixes: a8ba798bc8 ("selftests: enable O and KBUILD_OUTPUT")
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Reviewed-by: Darren Hart (VMware) <dvhart@infradead.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/futex/Makefile

@@ -14,7 +14,7 @@ all:
 	done
 
 override define RUN_TESTS
-	@if [ `dirname $(OUTPUT)` = $(PWD) ]; then ./run.sh; fi
+	$(OUTPUT)/run.sh
 endef
 
 override define INSTALL_RULE