tools/vm/slabinfo: Handle files in debugfs

tools/vm/slabinfo: Handle files in debugfs

Commit c3f4b3e8d49ee relocated and renamed the alloc_calls and
free_calls files from /sys/kernel/slab/NAME/*_calls over to
/sys/kernel/debug/slab/NAME/*_calls but didn't update the slabinfo tool
with the new location.

This change will now have slabinfo look at the new location (and filenames)
with a fallback to the prior files.

Fixes: c3f4b3e8d49ee ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Cc: stable@vger.kernel.org
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Tested-by: Stéphane Graber <stgraber@ubuntu.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>