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.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>