fs/ntfs3: Use kmalloc_array for allocating multiple elements

Prefer using kmalloc_array(a, b) over kmalloc(a * b) as this
improves semantics since kmalloc is intended for allocating an
array of memory.

Signed-off-by: Kenneth Lee <klee33@uw.edu>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>