ALSA: scarlett2: Add missing error check to scarlett2_usb_set_config()

scarlett2_usb_set_config() calls scarlett2_usb_get() but was not
checking the result. Return the error if it fails rather than
continuing with an invalid value.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Fixes: 9e15fae6 ("ALSA: usb-audio: scarlett2: Allow bit-level access to config")
Link: https://lore.kernel.org/r/def110c5c31dbdf0a7414d258838a0a31c0fab67.1703001053.git.g@b4.vu


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