ALSA: core: Constify the name in new kcontrols

We never modify it and this lets us use a const string as the name without
warnings.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Liam Girdwood <lrg@ti.com>