HID: prodikeys: remove a redundant forward declaration of struct pcmidi_snd

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/hid-prodikeys.c b/drivers/hid/hid-prodikeys.c
index 7563229..158b389 100644
--- a/drivers/hid/hid-prodikeys.c
+++ b/drivers/hid/hid-prodikeys.c
@@ -44,8 +44,6 @@
 	struct pcmidi_snd	*pm; /* pcmidi device context */
 };
 
-struct pcmidi_snd;
-
 struct pcmidi_sustain {
 	unsigned long		in_use;
 	struct pcmidi_snd	*pm;