initutils: use PRIu64 for uint64_t in setproctitle

initutils: use PRIu64 for uint64_t in setproctitle

Kernel UAPI provides as with the following declaration:
/*
 * This structure provides new memory descriptor
 * map which mostly modifies /proc/pid/stat[m]
 * output for a task. This mostly done in a
 * sake of checkpoint/restore functionality.
 */
struct prctl_mm_map {
	__u64	start_code;		/* code section bounds */
	__u64	end_code;
	__u64	start_data;		/* data section bounds */
	__u64	end_data;
	__u64	start_brk;		/* heap for brk() syscall */
	__u64	brk;
	__u64	start_stack;		/* stack starts at */
	__u64	arg_start;		/* command line arguments bounds */
	__u64	arg_end;
	__u64	env_start;		/* environment variables bounds */
	__u64	env_end;
	__u64	*auxv;			/* auxiliary vector */
	__u32	auxv_size;		/* vector size */
	__u32	exe_fd;			/* /proc/$pid/exe link file */
};

Let's use appropriate types/format specifiers everywhere.

Issue #4268

Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>