fs/ntfs3: Keep preallocated only if option prealloc enabled

If size of file was reduced, we still kept allocated blocks.
This commit makes ntfs3 work as other fs like btrfs.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=214719


Fixes: 4342306f ("fs/ntfs3: Add file operations and implementation")

Reported-by: Ganapathi Kamath <hgkamath@hotmail.com>
Tested-by: Ganapathi Kamath <hgkamath@hotmail.com>
Reviewed-by: Kari Argillander <kari.argillander@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>