afs: Remove second argument to afs_GetDSlot

afs: Remove second argument to afs_GetDSlot

All callers of afs_GetDSlot were passing NULL as the second argument
to afs_GetDSlot. So, remove the argument, and behave as if tmpdc was
NULL unconditionally.

Reviewed-on: http://gerrit.openafs.org/6416
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 12177ba6fffaf8a693dd8c8e9445d5e7725ae743)

Change-Id: Ic1ad6d35a7051e83a811692156b0da7207cb57f4
Reviewed-on: http://gerrit.openafs.org/7939
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>