fs/ntfs3: Add check for kmemdup

Since the kmemdup may return NULL pointer,
it should be better to add check for the return value
in order to avoid NULL pointer dereference.

Fixes: b46acd6a ("fs/ntfs3: Add NTFS journal")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>