cmd: osd: Depend on OSD

The OSD command calls functions from video_osd-uclass.o ,
which is built only when CONFIG_OSD is enabled. Add the
missing dependency into Kconfig.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 953e1f0..4ccb0ce 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1503,6 +1503,7 @@
 
 config CMD_OSD
 	bool "osd"
+	depends on OSD
 	help
 	  Enable the 'osd' command which allows to query information from and
 	  write text data to a on-screen display (OSD) device; a virtual device