MFC r232548:

MFC r232548:

Make growfs(8) mostly style compliant.  No functional changes,
verified with MD5.

MFC r232858:

After r232548, clang complains about the apparent '=-' operator (a
left-over from ancient C times, and a frequent typo) in growfs.c:

sbin/growfs/growfs.c:1550:8: error: use of unary operator that may be intended as compound assignment (-=) [-Werror]
        blkno =- 1;
              ^~

Use 'blkno = -1' instead, to silence the error.

git-svn-id: svn://svn.freebsd.org/base/stable/9@237497 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f