hwmon: (asc7621) make several arrays static const

Don't populate the arrays on the stack, instead make them static.
Makes the object code smaller by over 950 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  26144	  18768	    352	  45264	   b0d0	drivers/hwmon/asc7621.o

After:
   text	   data	    bss	    dec	    hex	filename
  25029	  18928	    352	  44309	   ad15	drivers/hwmon/asc7621.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>