platform/x86/intel-uncore-freq: Use uncore_index with read_control_freq

platform/x86/intel-uncore-freq: Use uncore_index with read_control_freq

Use the enumerated index for selecting the uncore driver parameter to
read, instead of reading everything. This is done in preparation to
expand the API to access more parameters later.

No functional change intended.

Signed-off-by: Tero Kristo <tero.kristo@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://lore.kernel.org/r/20240617060708.892981-5-tero.kristo@linux.intel.com
[ij: Removed underscores from variable names]
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>