rx: Get rid of some uneccessary temporary vars

rx: Get rid of some uneccessary temporary vars

rx_ReadProc and rx_ReadProc32 originally used temporary variables
(which were, at one time, declared as "register") to hand optimise
a couple of routines. With the removal of register throughout our
code, this is no longer helpful.

Change-Id: Id21a931408489b985b726af620a687b838303a86
Reviewed-on: http://gerrit.openafs.org/6997
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>