usb: audio-v2: Add uac2_effect_unit_descriptor definition

The UAC2 Effect Unit Descriptor has a slightly different definition
from other similar ones like Processing Unit or Extension Unit.
Define it here so that it can be used in USB-audio driver in a later
patch.
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200213112059.18745-2-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

include/linux/usb/audio-v2.h

@@ -156,6 +156,18 @@ struct uac2_feature_unit_descriptor {
 	__u8 bmaControls[0]; /* variable length */
 } __attribute__((packed));
 
+/* 4.7.2.10 Effect Unit Descriptor */
+
+struct uac2_effect_unit_descriptor {
+	__u8 bLength;
+	__u8 bDescriptorType;
+	__u8 bDescriptorSubtype;
+	__u8 bUnitID;
+	__le16 wEffectType;
+	__u8 bSourceID;
+	__u8 bmaControls[]; /* variable length */
+} __attribute__((packed));
+
 /* 4.9.2 Class-Specific AS Interface Descriptor */
 
 struct uac2_as_header_descriptor {