sh-vou: clarify videobuf2 dependency

The sh-vou driver has been converted from videobuf to videobuf2, but the Kconfig file still lists VIDEOBUF_DMA_CONTIG as a dependency. Consequently we can build the driver without VIDEOBUF2_DMA_CONTIG and get a link error:

drivers/built-in.o: In function `sh_vou_probe':
vf610-ocotp.c:(.text+0x2dbf5c): undefined reference to vb2_dma_contig_init_ctx' vf610-ocotp.c:(.text+0x2dc0b4): undefined reference to vb2_dma_contig_cleanup_ctx' vf610-ocotp.c:(.text+0x2dc144): undefined reference to vb2_dma_contig_memops' drivers/built-in.o: In function sh_vou_remove':
vf610-ocotp.c:(.text+0x2dc190): undefined reference to `vb2_dma_contig_cleanup_ctx'

This changes the dependency to VIDEOBUF2_DMA_CONTIG instead.

---
Found on ARM randconfig tests

index f88a6cfb7086..3ddf72f2d844 100644
@@ -38,7 +38,7 @@ config VIDEO_SH_VOU
 	depends on MEDIA_CAMERA_SUPPORT
 	depends on VIDEO_DEV && I2C && HAS_DMA
 	depends on ARCH_SHMOBILE || COMPILE_TEST
-	select VIDEOBUF_DMA_CONTIG
+	select VIDEOBUF2_DMA_CONTIG
 	help
 	  Support for the Video Output Unit (VOU) on SuperH SoCs.