block: bio: fix a warning at the kernel-doc markups

Using "@bio's parent" causes the following waring:
	./block/bio.c:10: WARNING: Inline emphasis start-string without end-string.

The main problem here is that this would be converted into:

	**bio**'s parent

By kernel-doc, which is not a valid notation. It would be
possible to use, instead, this kernel-doc markup:

	``bio's`` parent

Yet, here, is probably simpler to just use an altenative language:

	the parent of @bio
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

block/bio.c

@@ -327,7 +327,7 @@ static void bio_chain_endio(struct bio *bio)
 /**
  * bio_chain - chain bio completions
  * @bio: the target bio
- * @parent: the @bio's parent bio
+ * @parent: the parent bio of @bio
  *
  * The caller won't have a bi_end_io called when @bio completes - instead,
  * @parent's bi_end_io won't be called until both @parent and @bio have