tools/mm/thp_swap_allocator_test: fix small folio alignment

tools/mm/thp_swap_allocator_test: fix small folio alignment

Use ALIGNMENT_SMALLFOLIO instead of ALIGNMENT_MTHP when allocating small
folios to ensure correct memory alignment for the test case.

Before: test allocates small folios with 64KB alignment
(ALIGNMENT_MTHP) when only 4KB alignment (ALIGNMENT_SMALLFOLIO) is
needed.  This wastes address space and may cause allocation failures on
systems with fragmented memory.

Worst-case impact: this only affects thp_swap_allocator_test tool
behavior.

Link: https://lkml.kernel.org/r/20251209031745.2723120-1-kaushlendra.kumar@intel.com
Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>