media: cec: add stm32 driver

Missing stm32 directory to Makefile.
Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Fixes: 4be5e864 ("media: move CEC platform drivers to a separate directory")
Cc: <stable@vger.kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/cec/platform/Makefile

@@ -10,5 +10,6 @@ obj-$(CONFIG_CEC_MESON_AO)	+= meson/
 obj-$(CONFIG_CEC_SAMSUNG_S5P)	+= s5p/
 obj-$(CONFIG_CEC_SECO)		+= seco/
 obj-$(CONFIG_CEC_STI)		+= sti/
+obj-$(CONFIG_CEC_STM32)		+= stm32/
 obj-$(CONFIG_CEC_TEGRA)		+= tegra/