tools: gpio: Fix out-of-tree build regression

tools: gpio: Fix out-of-tree build regression

Commit 46353c3a72550 ("tools: gpio: Correctly add make dependencies for
gpio_utils") added a make rule for gpio-utils-in.o but used $(output)
instead of the correct $(OUTPUT) for the output directory, breaking
out-of-tree build (O=xx) with the following error:

  No rule to make target 'out/tools/gpio/gpio-utils-in.o', needed by 'out/tools/gpio/lsgpio-in.o'.  Stop.

Fix that.

Fixes: 46353c3a7255 ("tools: gpio: Correctly add make dependencies for gpio_utils")
Cc: <stable@vger.kernel.org>
Cc: Laura Abbott <labbott@redhat.com>
Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
Link: https://lore.kernel.org/r/20200325103154.32235-1-anssi.hannula@bitwise.fi
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>