ANDROID: Fix kernelci build-break on !CONFIG_CMA builds

commit c29070e5 ("ANDROID: GKI: cma: redirect page allocation to
CMA") added the field cma_alloc to struct zone if CONFIG_CMA. However,
two references to cma_alloc were added in mm/page_alloc.c that
could be reached if CONFIG_MEMORY_ISOLATION and CONFIG_COMPACTION
are defined.

Fixes: c29070e5 ("ANDROID: GKI: cma: redirect page allocation to CMA")
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: I3a4b803612084a070ba3cc0af11808bea20d324e