ASoC: rt1308: make array pd static const, makes object smaller

ASoC: rt1308: make array pd static const, makes object smaller

Don't populate the array pd on the stack but instead make it
static const. Makes the object code smaller by 82 bytes.

Before:
   text	   data	    bss	    dec	    hex	filename
  26548	   7288	     64	  33900	   846c	sound/soc/codecs/rt1308.o

After:
   text	   data	    bss	    dec	    hex	filename
  26370	   7384	     64	  33818	   841a	sound/soc/codecs/rt1308.o

(gcc version 9.2.1, amd64)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20190907074634.22144-1-colin.king@canonical.com
Signed-off-by: Mark Brown <broonie@kernel.org>