rx checkcall kill extra indirection on call for conn

rx checkcall kill extra indirection on call for conn

we already set a local variable, conn, to call->conn. use it instead
of dereferencing call->conn repeatedly

Change-Id: I5d38edc1d3507a717598140393094b1ba22ced46
Reviewed-on: http://gerrit.openafs.org/2113
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Derrick Brashear <shadow@dementia.org>