udf: Allocate name buffer in directory iterator on heap

udf: Allocate name buffer in directory iterator on heap

Currently we allocate name buffer in directory iterators (struct
udf_fileident_iter) on stack. These structures are relatively large
(some 360 bytes on 64-bit architectures). For udf_rename() which needs
to keep three of these structures in parallel the stack usage becomes
rather heavy - 1536 bytes in total. Allocate the name buffer in the
iterator from heap to avoid excessive stack usage.

Link: https://lore.kernel.org/all/202212200558.lK9x1KW0-lkp@intel.com
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>