nmeter: do not clamp down %Nc to minimum of 10 (think nmeter "%`nproc`c")

nmeter: do not clamp down %Nc to minimum of 10 (think nmeter "%`nproc`c")

Also, go for unsigned divisions.

function                                             old     new   delta
init_cpu                                              61      73     +12
collect_cpu                                          444     422     -22
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 12/-22)            Total: -10 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>