selftests/Makefile: make `run_tests' depend on `all'

So a "make run_tests" will build the tests before trying to run them.
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/Makefile

@@ -5,7 +5,7 @@ all:
 		make -C $$TARGET; \
 	done;
 
-run_tests:
+run_tests: all
 	for TARGET in $(TARGETS); do \
 		make -C $$TARGET run_tests; \
 	done;