docbook: fix command spacing

The total width of the command name plus spaces should be
8 characters, but were 7 and 9, respectively. With 8 chars,
all commands are now lining up nicely.

The mandocs, psdocs, xmldocs commands are OK.

Before:
  HOSTCC  scripts/basic/docproc
  DOCPROC Documentation/DocBook/deviceiobook.xml
  HTML   Documentation/DocBook/deviceiobook.html
  DOCPROC Documentation/DocBook/wanbook.xml
  PDF      Documentation/DocBook/wanbook.pdf

After:
  HOSTCC  scripts/basic/docproc
  DOCPROC Documentation/DocBook/deviceiobook.xml
  HTML    Documentation/DocBook/deviceiobook.html
  DOCPROC Documentation/DocBook/wanbook.xml
  PDF     Documentation/DocBook/wanbook.pdf
Signed-off-by: Hans Ulrich Niedermann <hun@n-dimensional.de>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>