futex: get rid of a kernel-docs build warning

Adjust whitespaces and blank lines in order to get rid of this:

	./kernel/futex.c:491: WARNING: Definition list ends without a blank line; unexpected unindent.
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/57788af7889161483e0c97f91c079cfb3986c4b3.1586881715.git.mchehab+huawei@kernel.orgSigned-off-by: NJonathan Corbet <corbet@lwn.net>

kernel/futex.c

@@ -486,10 +486,13 @@ static u64 get_inode_sequence_number(struct inode *inode)
  * The key words are stored in @key on success.
  *
  * For shared mappings (when @fshared), the key is:
+ *
  *   ( inode->i_sequence, page->index, offset_within_page )
+ *
  * [ also see get_inode_sequence_number() ]
  *
  * For private mappings (or when !@fshared), the key is:
+ *
  *   ( current->mm, address, 0 )
  *
  * This allows (cross process, where applicable) identification of the futex