mm/damon/sysfs-schemes: handle tried regions sysfs directory allocation failure

DAMOS tried regions sysfs directory allocation function
(damon_sysfs_scheme_regions_alloc()) is not handling the memory allocation
failure.  In the case, the code will dereference NULL pointer.  Handle the
failure to avoid such invalid access.

Link: https://lkml.kernel.org/r/20231106233408.51159-3-sj@kernel.org
Fixes: 9277d036

 ("mm/damon/sysfs-schemes: implement scheme region directory")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.2+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>