mm: compaction: correct the nr_strict va isolated check for CMA

mm: compaction: correct the nr_strict va isolated check for CMA

Thierry reported that the "iron out" patch for isolate_freepages_block()
had problems due to the strict check being too strict with "mm:
compaction: Iron out isolate_freepages_block() and
isolate_freepages_range() -fix1".  It's possible that more pages than
necessary are isolated but the check still fails and I missed that this
fix was not picked up before RC1.  This same problem has been identified
in 3.7-RC1 by Tony Prisk and should be addressed by the following patch.

Signed-off-by: Mel Gorman <[email protected]>
Tested-by: Tony Prisk <[email protected]>
Reported-by: Thierry Reding <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Richard Davies <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Avi Kivity <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>