src/splice-test.c: use memalign instead of aligned_alloc

src/splice-test.c: use memalign instead of aligned_alloc

The build fails on SLE11 as the function aligned_alloc is not
available there. Replace it by memalign that has the same semantics
and is commonly used in fstests code base. aligned_alloc has
additional requirements on the alignment and buffer size but that is
ok as the buffer is defined in multiples of the alignment.

Signed-off-by: David Sterba <dsterba@suse.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>