media: cx18: drop an unused macro

The macro p_to_snd_cx18_card() is just a variant for container_of(),
not actually used inside the code. So, drop it.

This address a clang warning.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/pci/cx18/cx18-alsa-main.c

@@ -51,12 +51,6 @@ struct snd_cx18_card *to_snd_cx18_card(struct v4l2_device *v4l2_dev)
 	return to_cx18(v4l2_dev)->alsa;
 }
 
-static inline
-struct snd_cx18_card *p_to_snd_cx18_card(struct v4l2_device **v4l2_dev)
-{
-	return container_of(v4l2_dev, struct snd_cx18_card, v4l2_dev);
-}
-
 static void snd_cx18_card_free(struct snd_cx18_card *cxsc)
 {
 	if (cxsc == NULL)