s390/diag: Diag204 add busy return errno

When diag204-busy-indication facility is installed, diag204 can return
'8' which means device is busy and no operation is done. Add check for
return codes of diag204 call. Return error codes according to diag204
return codes.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Tobias Huschle <huschle@linux.ibm.com>
Signed-off-by: Mete Durlu <meted@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>