wl128x-radio really depends on TI_ST

All other drivers using the TI_ST infrastructure use 'depends on' for this symbol, and it makes no sense to only enable that if CONFIG_NET is enable, because the radio driver also depends on CONFIG_NET itself:

ERROR: "skb_queue_purge" [drivers/media/radio/wl128x/fm_drv.ko] undefined!
ERROR: "skb_push" [drivers/media/radio/wl128x/fm_drv.ko] undefined!
ERROR: "skb_pull" [drivers/media/radio/wl128x/fm_drv.ko] undefined!

Making the driver dependency explicit solves randconfig build problems and makes it more obvious to the reader.

index f359be7e9dd9..9d6574bebf78 100644
@@ -5,7 +5,7 @@ menu "Texas Instruments WL128x FM driver (ST based)"
 config RADIO_WL128X
 	tristate "Texas Instruments WL128x FM Radio"
 	depends on VIDEO_V4L2 && RFKILL && GPIOLIB && TTY
-	select TI_ST if NET
+	depends on TI_ST
 	help
 	Choose Y here if you have this FM radio chip.