vfio-ccw: Fix the conversion of Format-0 CCWs to Format-1

When processing Format-0 CCWs, we use the "len" variable as the
number of CCWs to convert to Format-1.  But that variable
contains zero here, and is not a meaningful CCW count until
ccwchain_calc_length() returns.  Since that routine requires and
expects Format-1 CCWs to identify the chaining behavior, the
format conversion must be done first.

Convert the 2KB we copied even if it's more than we need.

Fixes: 7f8e89a8f2 ("vfio-ccw: Factor out the ccw0-to-ccw1 transition")
Reported-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20190702180928.18113-1-farman@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

drivers/s390/cio/vfio_ccw_cp.c

@@ -431,7 +431,7 @@ static int ccwchain_handle_ccw(u32 cda, struct channel_program *cp)
 
 	/* Convert any Format-0 CCWs to Format-1 */
 	if (!cp->orb.cmd.fmt)
-		convert_ccw0_to_ccw1(cp->guest_cp, len);
+		convert_ccw0_to_ccw1(cp->guest_cp, CCWCHAIN_LEN_MAX);
 
 	/* Count the CCWs in the current chain */
 	len = ccwchain_calc_length(cda, cp);