kthread: switch to new kerneldoc syntax for named variable macro argument

The syntax without dots is available since commit 43756e34
("scripts/kernel-doc: Add support for named variable macro arguments").

The same HTML output is produced with and without this patch.

Link: https://lkml.kernel.org/r/20210513161702.1721039-1-j.neuschaefer@gmx.net


Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>