blk-throttle: Only use seq_printf() in tg_prfill_limit()

Currently tg_prfill_limit() uses a combination of snprintf() and strcpy()
to generate the values parts of the limits string, before passing them as
arguments to seq_printf().

Convert to use only a sequence of seq_printf() calls per argument, which is
simpler.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240327094020.3505514-1-john.g.garry@oracle.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>