scmi_perf/perf_protocol_ops: Fix get_dvfs_dependency_id

get_dvfs_dependency_id() wrongly returns an element index that
refers to the logical, not the physical domain.

Fix the function by returning the respective dependency (physical)
domain for the logical domain.

Reported-by: Ionela Voinescu <ionela.voinescu@arm.com>
Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>
Change-Id: I923a338beece05ffc4037d2913fdcbab5265aa45