gpio: fix test.py for gpio label lookup

commit 2bd261dd1712 ("gpio: search for gpio label if gpio is not found through bank name")

disabled DM_GPIO_LOOKUP_LABEL which is needed
in sandbox defconfigs, as we have tests for this
functionality.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 57218ac..8cf2ad5 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -117,6 +117,7 @@
 CONFIG_DMA_CHANNELS=y
 CONFIG_SANDBOX_DMA=y
 CONFIG_GPIO_HOG=y
+CONFIG_DM_GPIO_LOOKUP_LABEL=y
 CONFIG_PM8916_GPIO=y
 CONFIG_SANDBOX_GPIO=y
 CONFIG_DM_HWSPINLOCK=y