regulator: stm32-booster: Fix W=1 build warning when CONFIG_OF=n

Fix below warning when CONFIG_OF=n:

drivers/regulator/stm32-booster.c:104:34: warning: ‘stm32_booster_of_match’ defined but not used [-Wunused-const-variable=]
  104 | static const struct of_device_id stm32_booster_of_match[] = {
      |                                  ^~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Acked-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Link: https://lore.kernel.org/r/20200821111943.29b2b4ca@xhacker.debianSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/stm32-booster.c

@@ -101,7 +101,7 @@ static int stm32_booster_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static const struct of_device_id stm32_booster_of_match[] = {
+static const struct of_device_id __maybe_unused stm32_booster_of_match[] = {
 	{
 		.compatible = "st,stm32h7-booster",
 		.data = (void *)&stm32h7_booster_desc