fs/ntfs3: Remove a useless test

'new_free' has just been allocated by kmalloc() and is known to be not
NULL.
So this pointer can't be equal to a previous memory allocation.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>