media: cx23885: make const array buf static, reduces object code size

Don't populate the array buf on the stack, instead make it static.
Makes the object code smaller by over 240 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  21689	  22992	    416	  45097	   b029	cx23885-cards.o

After:
   text	   data	    bss	    dec	    hex	filename
  21348	  23088	    416	  44852	   af34	cx23885-cards.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>