s390/cio: Fix incorrect xsch opcode specification

The numeric representation of the xsch instruction was incorrectly
specified, resulting in reserved fields of the instruction opcode
potentially being set to a non-zero value. While this doesn't currently
cause any problem, a future architecture might make use of these fields
so that the current specification could result in an exception or
unwanted side-effects.

Fix this by using the xsch instruction code for which support in
binutils was added in 2003.

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>