xprtrdma: Clean up xprt_rdma_print_stats()

checkpatch.pl complained about the seq_printf() format string split
across lines and the use of %Lu.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Devesh Sharma <devesh.sharma@avagotech.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>