s390/cio: fix multiple structure definitions

Fix multiple definitions of struct channel_path_desc by moving it
to asm/chpid.h . Also change ccw_device_get_chp_desc to use proper
types.

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