ALSA: scarlett2: Add missing error check to scarlett2_config_save()

ALSA: scarlett2: Add missing error check to scarlett2_config_save()

scarlett2_config_save() was ignoring the return value from
scarlett2_usb(). As this function is not called from user-space we
can't return the error, so call usb_audio_err() instead.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Fixes: 9e4d5c1be21f ("ALSA: usb-audio: Scarlett Gen 2 mixer interface")
Link: https://lore.kernel.org/r/bf0a15332d852d7825fa6da87d2a0d9c0b702053.1703001053.git.g@b4.vu
Signed-off-by: Takashi Iwai <tiwai@suse.de>