cmn_rhodes: change the way hnf_count is being used

`hnf_count` context member holds the count of HN-F nodes in the
interconnect mesh. To program the SCG registers with the correct HN-F
node ids and count when CAL mode is enabled, `hnf_count` has been
decremented while processing all odd numbered HN-F node ids. This might
give a wrong HN-F count, if the context member is used at the later
stage. So instead of decrementing the count, use a separate variable
when programming the SCG registers allowing correct value of `hnf_count`
retained all over the module.

Change-Id: I5e8da78ccc224776846bfd76b7c4bc7dc5637dfb
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>