mm/zsmalloc: don't fail if can't create debugfs info

Change the return type of zs_pool_stat_create() to void, and remove the
logic to abort pool creation if the stat debugfs dir/file could not be
created.

The debugfs stat file is for debugging/information only, and doesn't
affect operation of zsmalloc; there is no reason to abort creating the
pool if the stat file can't be created.  This was seen with zswap, which
used the same name for all pool creations, which caused zsmalloc to fail
to create a second pool for zswap if CONFIG_ZSMALLOC_STAT was enabled.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Dan Streetman <dan.streetman@canonical.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>