powerpc/vas: Report proper error code for address translation failure

P9 DD2 NX workbook (Table 4-36) says DMA controller uses CC=5
internally for translation fault handling. NX reserves CC=250 for
OS to notify user space when NX encounters address translation
failure on the request buffer. Not an issue in earlier releases
as NX does not get faults on kernel addresses.

This patch defines CSB_CC_FAULT_ADDRESS(250) and updates CSB.CC with
this proper error code for user space.

Fixes: c96c4436

 ("powerpc/vas: Update CSB and notify process for fault CRBs")
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
[mpe: Added Fixes tag and fix typo in comment]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/019fd53e7538c6f8f332d175df74b1815ef5aa8c.camel@linux.ibm.com