genwqe: fix MAX_ORDER usage

MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
can deliver is MAX_ORDER-1.

Fix MAX_ORDER usage in genwqe driver.

Link: https://lkml.kernel.org/r/20230315113133.11326-6-kirill.shutemov@linux.intel.com


Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Frank Haverkamp <haver@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>