blktrace: Fix new kernel-doc warnings

blktrace: Fix new kernel-doc warnings

Fix blktrace.c kernel-doc warnings:
 Warning(kernel/trace/blktrace.c:858): No description found for parameter 'ignore'
 Warning(kernel/trace/blktrace.c:890): No description found for parameter 'ignore'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100529114507.c466fc1e.randy.dunlap@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>