ALSA: drivers: make array 'names' const, reduces object code size

Don't populate array 'names' on the stack but instead make them static.
Makes the object code smaller by 50 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  21237	   9192	   1120	  31549	   7b3d	linux/sound/drivers/dummy.o

After:
   text	   data	    bss	    dec	    hex	filename
  21095	   9280	   1120	  31495	   7b07	linux/sound/drivers/dummy.o

(gcc version 7.2.0 x86_64)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>