USBAudio: Add endstr check before reading each capability

If there is extra Altset in section of last playback profile,
the following profile of capture would be read as playback profile.

Fix it by adding endstr check before reading string beginning of
Channel/Sample Rate/Format and use "Altset " to parse profile
instead of "Altset".

Change-Id: I05fc7c27a0ca2ada9427146bad85a1da7ab6206f
1 file changed