ALSA: scarlett2: Infer has_msd_mode from config items

Rather than storing has_msd_mode in the per-device structure, infer
this from the presence of the SCARLETT2_CONFIG_MSD_SWITCH entry in the
device's configuration set.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/ecbf3740e6b30a245333528ae4c504f37a9bc6bf.1703444932.git.g@b4.vu


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