block/bfq: update comments and default value in docs for fifo_expire

Correct the comments since bfq_fifo_expire[0] is for async request,
while bfq_fifo_expire[1] is for sync request.
Also update docs, according the source code, the default
fifo_expire_async is 250ms, and fifo_expire_sync is 125ms.

Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: josephhz

Documentation/block/bfq-iosched.rst

@@ -430,13 +430,13 @@ fifo_expire_async
 -----------------
 
 This parameter is used to set the timeout of asynchronous requests. Default
-value of this is 248ms.
+value of this is 250ms.
 
 fifo_expire_sync
 ----------------
 
 This parameter is used to set the timeout of synchronous requests. Default
-value of this is 124ms. In case to favor synchronous requests over asynchronous
+value of this is 125ms. In case to favor synchronous requests over asynchronous
 one, this value should be decreased relative to fifo_expire_async.
 
 low_latency

block/bfq-iosched.c

@@ -162,7 +162,7 @@ BFQ_BFQQ_FNS(split_coop);
 BFQ_BFQQ_FNS(softrt_update);
 #undef BFQ_BFQQ_FNS						\
 
-/* Expiration time of sync (0) and async (1) requests, in ns. */
+/* Expiration time of async (0) and sync (1) requests, in ns. */
 static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
 
 /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */