ALSA: usb-audio: Stop both endpoints properly at error

start_endpoints() may leave the data endpoint running if an error
happens at starting the sync endpoint.  We should stop both streams
properly, instead.

While we're at it, move the debug prints into the endpoint.c that is a
more suitable place.

Tested-by: Keith Milner <kamilner@superlative.org>
Tested-by: Dylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-22-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>