libafs: check afs_InitReq return code

Do not ignore the return code from afs_InitReq everywhere it is
called. If afs_InitReq fails, the vrequest could not be initialized
for some reason.

Reviewed-on: http://gerrit.openafs.org/11097
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit cdbf49f06baf33abd803b5d1ec245e58a94eec52)

Change-Id: Ia8c0368f50f77b148a1e3f41b0538b0ec7c4123d
Reviewed-on: http://gerrit.openafs.org/11163
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Gergely Madarasz <madaraszg@gmail.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>