usb: gadget: f_uac1: Change volume name and remove alt names

usb: gadget: f_uac1: Change volume name and remove alt names

This changes the UAPI to align with disussion of alt settings work.

fu_name is renamed to fu_vol_name, and alt settings mode names
are removed for now in favor of future work where they will be
settable in subdirectories for each alt mode.

discussion thread for api changes for alt mode settings:
https://lore.kernel.org/linux-usb/35be4668-58d3-894a-72cf-de1afaacae45@ivitera.com/T/

Signed-off-by: Chris Wulff <crwulff@gmail.com>
Link: https://lore.kernel.org/r/20240804002912.3293177-2-crwulff@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>