Revert "ALSA: usb-audio: Always initialize fixed_rate in snd_usb_find_implicit_fb_sync_format()"

This reverts commit bfd36b1d which is
commit 291e9da9 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I087bfd704d03c5aef4cf14d6130d0c310ea9313a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>