scripts/kernel-doc: fix empty function description section

scripts/kernel-doc mishandles a function that has a multi-line function
short description and no function parameters.  The observed problem was
from drivers/scsi/scsi_netlink.c:

/**
 * scsi_netlink_init - Called by SCSI subsystem to intialize
 * 	the SCSI transport netlink interface
 *
 **/

kernel-doc treated the " * " line as a Description: section with only a
newline character in the Description contents.  This caused
output_highlight() to complain: "output_highlight got called with no
args?", plus produce a perl call stack backtrace.

The fix is just to ignore Description sections if they only contain "\n".

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>