staging: lustre: ptlrpc: silence a shift wrapping warning
"svcpt->scp_hist_seq" is a u64 so static checkers complain that 1U
should be 1ULL. I looked at REQS_SEQ_SHIFT() a little and it seems to
be capped by the number of CPUs online and the amount of memory, but I
think it could go above 32 possibly.