gpio: 104-idi-48e: make array register_offset static, makes object smaller

Don't populate the array register_offset on the stack but instead make it
static. Makes the object code smaller by 63 bytes.  Also add the int type
specifier to clean up a checkpatch warning.

Before:
   text	   data	    bss	    dec	    hex	filename
   9212	   5712	   1408	  16332	   3fcc	drivers/gpio/gpio-104-idi-48.o

After:
   text	   data	    bss	    dec	    hex	filename
   9085	   5776	   1408	  16269	   3f8d	drivers/gpio/gpio-104-idi-48.o

(gcc version 9.2.1, amd64)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>