Despite being exported, there's no prototype for it at the
headers, as warned by sparse:

Fixes this sparse warning:
	drivers/media/platform/ti-vpe/vpdma.c:1000:6: warning: no previous prototype for 'vpdma_enable_list_notify_irq' [-Wmissing-prototypes]
	 void vpdma_enable_list_notify_irq(struct vpdma_data *vpdma, int irq_num,
	      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Worse than that, it is not even used, as making it static it
would produce:

	drivers/media/platform/ti-vpe/vpdma.c:1000:13: warning: 'vpdma_enable_list_notify_irq' defined but not used [-Wunused-function]
	 static void vpdma_enable_list_notify_irq(struct vpdma_data *vpdma, int irq_num,
	             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

So, let's just get rid of the dead code. If needed in the future,
someone could re-add it.

Cc: Benoit Parrot <bparrot@ti.com>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>