partx: don't print error when partition already doesn't exist

partx: don't print error when partition already doesn't exist

If you run partx -d to delete partitions, and there are gaps
in the sequence ( partition 2 exists, but 1 doesn't ), then it
would complain that it had errors trying to remove the partitions
that already don't exist. Changed to ignore the error when
errno == ENXIO.

Signed-off-by: Phillip Susi <psusi@cfl.rr.com>