docs: Fix formatting of literal sections in fanotify docs

Stephen Rothwell reported the following warning was introduced by commit
c0baf9ac0b05 ("docs: Document the FAN_FS_ERROR event").

Documentation/admin-guide/filesystem-monitoring.rst:60: WARNING:
Definition list ends without a blank line; unexpected unindent.

Link: https://lore.kernel.org/r/87y26camhe.fsf@collabora.com
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jan Kara <jack@suse.cz>

docs: Document the FAN_FS_ERROR event

Document the FAN_FS_ERROR event for user administrators and user space
developers.

Link: https://lore.kernel.org/r/20211025192746.66445-32-krisman@collabora.com
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>