input: sur40: fix v4l dependency

The recently added support for the raw video stream in the SUR40 driver fails to link if the driver is built-in but v4l2 is not:

drivers/built-in.o: In function `sur40_disconnect':
:(.text+0xf2ed2): undefined reference to video_unregister_device' :(.text+0xf2eda): undefined reference to v4l2_device_unregister' :(.text+0xf2ee2): undefined reference to `vb2_dma_sg_cleanup_ctx'

This adds an explicit dependency, to avoid the broken build.

index cee8ffe4ffd9..90935f3918db 100644
@@ -980,6 +980,7 @@ config TOUCHSCREEN_SUN4I
 config TOUCHSCREEN_SUR40
 	tristate "Samsung SUR40 (Surface 2.0/PixelSense) touchscreen"
 	depends on USB && MEDIA_USB_SUPPORT && HAS_DMA
+	depends on VIDEO_V4L2
 	select INPUT_POLLDEV
 	select VIDEOBUF2_DMA_SG
 	help