tools/vm/slabinfo: fix sanity checks enabling

tools/vm/slabinfo: fix sanity checks enabling

The sysfs file name for enabling sanity checking is called
'sanity_checks' and not 'sanity'.

The name of the file has never changed since the introduction of the
slub allocator.  Obviously, most people turn the checks on via the
command line option and not during runtime using slabinfo.

Link: http://lkml.kernel.org/r/20200116131642.642-1-dwagner@suse.de
Signed-off-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Tobin C. Harding" <tobin@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>