pinctrl: stm32: Fix compile testing selection

While selecting the driver for compile testing seemed possible,
the driver was not compiled because the driver directory was only
added if ARCH_STM32 was selected.

This patch now makes the pinctrl Makefile to add stm32 directory if
PINCTRL_STM32 is selected.
Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/Makefile

@@ -46,7 +46,7 @@ obj-$(CONFIG_ARCH_QCOM)		+= qcom/
 obj-$(CONFIG_PINCTRL_SAMSUNG)	+= samsung/
 obj-$(CONFIG_PINCTRL_SH_PFC)	+= sh-pfc/
 obj-$(CONFIG_PINCTRL_SPEAR)	+= spear/
-obj-$(CONFIG_ARCH_STM32)	+= stm32/
+obj-$(CONFIG_PINCTRL_STM32)	+= stm32/
 obj-$(CONFIG_PINCTRL_SUNXI)	+= sunxi/
 obj-$(CONFIG_PINCTRL_UNIPHIER)	+= uniphier/
 obj-$(CONFIG_ARCH_VT8500)	+= vt8500/