bootcount: fix printf() code

bootcount: fix printf() code

For printing phys_addr_t we should use %pa to avoid warning like:

drivers/bootcount/bootcount_syscon.c:110:17: note: in expansion of macro ‘dev_err’
  110 |                 dev_err(dev, "%s: Unsupported register size: %d\n", __func__,
      |                 ^~~~~~~

seen for sandbox_defconfig with CONFIG_PHYS_64BIT=y.

Cf. commit 1eebd14b7902 ("vsprintf: Add modifier for phys_addr_t")

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>