kernel/ddb: Fix formatting when printing command tables.

kernel/ddb: Fix formatting when printing command tables.

FreeBSD's r163134:

Fixed formatting of printing of command tables.  With the default max
output width of 79, only 6 columns of width 12 each fit, but 7 columns
were printed.

The fix is to pass the width of the next output to db_end_line() and
not assume there that this width is always 1.

Related unfixed bugs:
- 1 character is wasted for a space after the last column
- suppression of trailing spaces used to limit the misformatting, but
  seems to have been lost
- in db_examine(), the width of the next output is not known and is
  still assumed to be 1.

Taken-from: FreeBSD