cmn700: ccg: do bound check while getting ldid

get_ldid function returns the ldid based on the state of the port
aggregation. To avoid any potential buffer overflow, do boundary check
of ldid value with the total CCG node count.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I0c31484ccb00fa21ff25538206d27073e7fa1f41