lib/test_meminit: fix off-by-one error in test_pages()

commit efb78fa8 ("lib/test_meminit: allocate pages up to order
MAX_ORDER") works great in kernels 6.4 and newer thanks to commit
23baf831 ("mm, treewide: redefine MAX_ORDER sanely"), but for older
kernels, the loop is off by one, which causes crashes when the test
runs.

Fix this up by changing "<= MAX_ORDER" "< MAX_ORDER" to allow the test
to work properly for older kernel branches.

Fixes: 7ad44409

 ("lib/test_meminit: allocate pages up to order MAX_ORDER")
Cc: Andrew Donnellan <ajd@linux.ibm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Xiaoke Wang <xkernel.wang@foxmail.com>
Cc: <stable@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>