afs_bypasscache: parameters of afs_ReadNoCache can't be null

afs_bypasscache: parameters of afs_ReadNoCache can't be null

The first two parameters of afs_ReadNoCache() are unconditionally
indirected through, and all existing callers appear to guarantee
that these parameters are in fact non-null, so annotate the function
declaration to so indicate, and remove the one test that checks
whether avc (the first parameter) is null.  I suspect that acred
cannot be null either, but this code does not appear to depend on
that, so it's not included in the non-null annotation.

Change-Id: I496c868ffcbc9b894f91578019bc30bf7b14fefd
Reviewed-on: http://gerrit.openafs.org/7837
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>