pfctl: fix superblock printf format mismatch

It is impossible to compile pfctl with OPT_DEBUG due to integer width mismatch:

/usr/home/kajetan.staszkiewicz/freebsd.git/sbin/pfctl/pfctl_optimize.c:1479:9: error: format specifies type 'unsigned int' but the argument has type 'unsigned long' [-Werror,-Wformat]

					    i - pf_rule_desc[closest].prf_off--- pfctl_optimize.o ---

^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/home/kajetan.staszkiewicz/freebsd.git/sbin/pfctl/pfctl_optimize.c:52:44: note: expanded from macro 'DEBUG'

		printf("%s: " str "\n", __FUNCTION__ , ## v)
			      ~~~                         ^

1 error generated.

Reviewed by: kp
Obtained from: OpenBSD (pfctl_optimize.c 1.15)
Differential Revision: https://reviews.freebsd.org/D38918