Fix architectures where pointer and u_int have different sizes

[lwhsu]

Summary

r328383 seems breaking architectures where pointer and u_int have different
sizes:

https://ci.freebsd.org/job/FreeBSD-head-mips64-build/105/console

00:03:54.601 cc1: warnings being treated as errors
00:03:54.601 /usr/src/sbin/fsck_ffs/fsutil.c: In function 'flush':
00:03:54.601 /usr/src/sbin/fsck_ffs/fsutil.c:372: warning: cast from pointer to integer of different size
00:03:54.601 /usr/src/sbin/fsck_ffs/fsutil.c:372: warning: cast from pointer to integer of different size

[imp]

This is the right fix.

[delphij]

head/sbin/fsck_ffs/fsutil.c

372

I'm not 100% sure if this is correct.

I _think_ the intention was to give on-disk address (probably b_bno) as the memory pointer is less useful for debugging purposes since we are about to abort.

Looking at the context, it seems this is really an assertion that flush() is called with &sblk for BT_SUPERBLK, is this a valid assertion for setup.c:244? (I haven't worked on fsck for quite a few years so it's probably a good idea to defer this to McKusick).

[mckusick]

This is the correct fix.