mm/page_alloc.c: clean code by merging two functions

mm/page_alloc.c: clean code by merging two functions

finalise_ac() is just 'epilogue' for 'prepare_alloc_pages'.  Therefore
there is no need to keep them both so 'finalise_ac' content can be merged
into prepare_alloc_pages() code.  It would make __alloc_pages_nodemask()
cleaner when it comes to readability.

Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@kernel.org>
Link: https://lkml.kernel.org/r/20200916110118.6537-1-mateusznosek0@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>