iommu/dma: Fix NEED_SG_DMA_LENGTH dependency

IOMMU_DMA does indeed depend on scatterlists having a DMA length, but
the NEED_SG_DMA_LENGTH symbol should be selected, not depended upon.
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/Kconfig

@@ -51,9 +51,9 @@ config OF_IOMMU
 # IOMMU-agnostic DMA-mapping layer
 config IOMMU_DMA
 	bool
-	depends on NEED_SG_DMA_LENGTH
 	select IOMMU_API
 	select IOMMU_IOVA
+	select NEED_SG_DMA_LENGTH
 
 config FSL_PAMU
 	bool "Freescale IOMMU support"