If an unmapped region was found and the flag is MS_ASYNC (without
MS_INVALIDATE) there is nothing to do and the result would be always
-ENOMEM, so return immediately.

Link: https://lkml.kernel.org/r/20201025092901.56399-1-sh1r4s3@mail.si-head.nlSigned-off-by: NNikita Ermakov <sh1r4s3@mail.si-head.nl>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>