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

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: I305a3aab7c80efe153cb3e14d060d883d3637ab3
Fixes: 132fcb460839 ("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/torvalds/linux.git
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>