automake: fix buildtest patch

Add check_PROGRAMS as a dependency of buildtest-TESTS target.
This is required because according to the official automake
documentation [1]:
* TESTS: contains all the tests files
* check_PROGRAMS: contains the programs used by the tests
* check_PROGRAMS is not automatically added to TESTS

So, by using only TESTS as a dependency for buildtest-TESTS we may end
up having runtime errors because of missing program required by the
tests.

[1]: https://www.gnu.org/software/automake/manual/html_node/Scripts_002dbased-Testsuites.html



Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit ee3e2af4)
Signed-off-by: Steve Sakoman <steve@sakoman.com>