package/exfatprogs: fix 64-bit types printf compile failure

Fixes:

  - http://autobuild.buildroot.net/results/a7364a6b3801d7d18c30c7242c6faf19431fddfd



  mkfs.c:60:14: error: format '%llu' expects argument of type 'long long unsigned int', but argument 2 has type 'long unsigned int' [-Werror=format=]
    exfat_debug("Volume Length(sectors) : %llu\n",
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>