s390/smp: fix cpu re-scan vs. cpu state

The cpu-info array starts with a list of cpus in configured state,
followed by the cpus in standby state. The comparison to decide which
state a cpu has is incorrect, this causes configured cpus appear as
standby cpus. The correct comparison is the index of the new cpu in
the cpu-info array vs. the number of configured cpus.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>