s390x/css: Make CCWDeviceClass::realize return bool

s390x/css: Make CCWDeviceClass::realize return bool

Since the realize() handler of CCWDeviceClass takes an 'Error **'
argument, best practices suggest to return a bool. See the api/error.h
Rules section. While at it, modify the call in s390_ccw_realize().

Signed-off-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20240522170107.289532-3-clg@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>