usb: gadget: u_audio: remove caching of stream buffer parameters

There is no necessity to copy PCM stream ring buffer area and size
properties to UAC private data structure, these values can be got
from substream itself.

The change gives more control on substream and avoid stale caching.

Change-Id: I91a2276b8eeb8f4961c06254240986301af30099
Fixes: 132fcb46 ("usb: gadget: Add Audio Class 2.0 Driver")
Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Git-commit: 96afb54ece0ee903d23a7ac04ddc461413b972c4
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git


Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>