kernel-doc: prevent duplicate description: output

Prevent duplicate output of a Description: section when there is a "blank"
("*") line between the initial function name/description line and the
"Description:" header.

Test case:  drivers/scsi/scsi_devinfo.c::scsi_init_devinfo().

Rob Landley hit this while he was producing SCSI kernel-doc.

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>