Cleanup: setting an outstanding error on a mapping was open coded too many
times.  Factor it out in mapping_set_error().
Signed-off-by: NGuillaume Chazarain <guichaz@yahoo.fr>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>