fscache: Fix some kerneldoc warnings shown up by W=1

fscache: Fix some kerneldoc warnings shown up by W=1

Fix some kerneldoc warnings in the fscache driver that are shown up by W=1.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Mauro Carvalho Chehab <mchehab@kernel.org>
cc: linux-fsdevel@vger.kernel.org
cc: linux-doc@vger.kernel.org
Link: https://lore.kernel.org/r/163214005516.2945267.7000234432243167892.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/163281899704.2790286.9177774252843775348.stgit@warthog.procyon.org.uk/