usb: gadget: f_uac2: fix endianness of 'struct cntrl_*_lay3'

The list [1] of commits doing endianness fixes in USB subsystem is long
due to below quote from USB spec Revision 2.0 from April 27, 2000:

------------
8.1 Byte/Bit Ordering

Multiple byte fields in standard descriptors, requests, and responses
are interpreted as and moved over the bus in little-endian order, i.e.
LSB to MSB.
------------

This commit belongs to the same family.

[1] Example of endianness fixes in USB subsystem:
commit 14e1d56c ("usb: gadget: f_uac2: endianness fixes.")
commit 42370b82 ("usb: gadget: f_uac1: endianness fixes.")
commit 63afd5cc ("USB: chaoskey: fix Alea quirk on big-endian hosts")
commit 74098c4a ("usb: gadget: acm: fix endianness in notifications")
commit cdd7928d ("ACM gadget: fix endianness in notifications")
commit 323ece54 ("cdc-wdm: fix endianness bug in debug statements")
commit e102609f ("usb: gadget: uvc: Fix endianness mismatches")
       list goes on

Fixes: 132fcb46 ("usb: gadget: Add Audio Class 2.0 Driver")
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>