C99 specifies the 't' length modifier type for pointer difference.
barebox vsnprintf supports it, thus use it.

We are guaranteed sizeof(long) == sizeof(void *) in barebox, so this
doesn't make a difference in practice except that it silences
following GCC warning:

  ./drivers/gpio/gpiolib.c: In function 'gpioinfo_request':
  ./include/printk.h:77:43: warning: format '%ld' expects argument of
     type 'long int', but argument 3 has type 'int' [-Wformat=]
  ...
  ./barebox-stm32/drivers/gpio/gpiolib.c:89:3: note: in expansion of macro 'pr_err'
     89 |   pr_err("_gpio_request: gpio-%ld (%s) status %d\n",

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>