jfs: Fix inconsistency between memory allocation and ea_buf->max_size

jfs: Fix inconsistency between memory allocation and ea_buf->max_size

CVE-2018-12233

The code is assuming the buffer is max_size length, but we weren't
allocating enough space for it.

Signed-off-by: Shankara Pailoor <shankarapailoor@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
(cherry picked from commit 92d34134193e5b129dc24f8d79cb9196626e8d7a)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>