[S390] cio: handle ssch() return codes correctly.

ssch() has two classes of return codes:
- condition codes (0-3) which need to be translated to Linux
  error codes
- Linux error codes (-EIO on exceptions) which should be passed
  to the caller (instead of erronously being handled like
  condition code 3)

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>