jffs2: reduce stack usage in jffs2_build_xattr_subsystem()

jffs2: reduce stack usage in jffs2_build_xattr_subsystem()

Use kcalloc() for allocation/flush of 128 pointers table to
reduce stack usage.

Function now returns -ENOMEM or 0 on success.

stackusage
Before:
./fs/jffs2/xattr.c:775  jffs2_build_xattr_subsystem     1208
dynamic,bounded

After:
./fs/jffs2/xattr.c:775  jffs2_build_xattr_subsystem     192
dynamic,bounded

Also update definition when CONFIG_JFFS2_FS_XATTR is not enabled

Tested with an MTD mount point and some user set/getfattr.

Many current target on OpenWRT also suffer from a compilation warning
(that become an error with CONFIG_WERROR) with the following output:

fs/jffs2/xattr.c: In function 'jffs2_build_xattr_subsystem':
fs/jffs2/xattr.c:887:1: error: the frame size of 1088 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
  887 | }
      | ^

Using dynamic allocation fix this compilation warning.

Fixes: c9f700f840bd ("[JFFS2][XATTR] using 'delete marker' for xdatum/xref deletion")
Reported-by: Tim Gardner <tim.gardner@canonical.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Ron Economos <re@w6rz.net>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Cc: stable@vger.kernel.org
Message-Id: <20230506045612.16616-1-ansuelsmth@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>