ALSA: usb-audio - Add ignore_ctl_error parameter

Added the ignore_ctl_error parameter to enable/disable the control-error
handling for mixer interfaces.  It was a hard-coded ifdef, and now you
can change it more easily.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>