rx: Don't double check conn->call

rx: Don't double check conn->call

We currently have

call = conn->call[channel]
if (call) {
   ...
} else {
    call = conn->call[channel]
    if (call) {
       ...
    }
}

As we don't drop (or acquire) any locks between the first and the
second check of call, there's no way that the result can be different
from the first time we checked. So just get rid of the uneccessary
code, and reindent the following block to match.

Change-Id: If21a1d0af461fe0c0651e713dfb99a7c5f01cba4
Reviewed-on: http://gerrit.openafs.org/8290
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>