dmaengine: stm32-dma: Fix typo in Kconfig

As STM32 DMA driver is only used as buit-in driver, it couldn't be used as
module.
Signed-off-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
Reviewed-by: Ludovic BARRE <ludovic.barre@st.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/Kconfig

@@ -458,7 +458,7 @@ config STM32_DMA
 	help
 	  Enable support for the on-chip DMA controller on STMicroelectronics
 	  STM32 MCUs.
-	  If you have a board based on such a MCU and wish to use DMA say Y or M
+	  If you have a board based on such a MCU and wish to use DMA say Y
 	  here.
 
 config S3C24XX_DMAC