dmaengine: stm32_mdma: add CONFIG_OF dependency

Without CONFIG_OF we get a build warning:

warning: (STM32_MDMA) selects DMA_OF which has unmet direct dependencies (DMADEVICES && OF)

This adds a dependency on CONFIG_OF. Since this means
we no longer need to select 'DMA_OF', I'm dropping that line
as well.

Fixes: a4ffb13c ("dmaengine: Add STM32 MDMA driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/Kconfig

@@ -495,8 +495,8 @@ config STM32_DMAMUX
 config STM32_MDMA
 	bool "STMicroelectronics STM32 master dma support"
 	depends on ARCH_STM32 || COMPILE_TEST
+	depends on OF
 	select DMA_ENGINE
-	select DMA_OF
 	select DMA_VIRTUAL_CHANNELS
 	help
 	  Enable support for the on-chip MDMA controller on STMicroelectronics