ocfs2: checking the wrong variable in ocfs2_move_extent()

"new_phys_cpos" is always a valid pointer here.
ocfs2_probe_alloc_group() allocates "*new_phys_cpos".

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Joel Becker <jlbec@evilplan.org>