V4L/DVB (5406): Add comment why the symbols are exported.

It is not immediately obvious why the ivtv symbols are exported
in ivtv-driver.c since both ivtv-fb and the IR-blaster module
are still out-of-tree, currently being ported to be in kernel.

Added a comment so people are aware of these issues.
Signed-off-by: NHans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/ivtv/ivtv-driver.c

@@ -1356,6 +1356,8 @@ static void module_cleanup(void)
 	pci_unregister_driver(&ivtv_pci_driver);
 }
 
+/* Note: These symbols are exported because they are used by the ivtv-fb
+   framebuffer module and an infrared module for the IR-blaster. */
 EXPORT_SYMBOL(ivtv_set_irq_mask);
 EXPORT_SYMBOL(ivtv_cards_active);
 EXPORT_SYMBOL(ivtv_cards);