Instead of copying pieces of variant-specific data (struct
icc_bwmon_data) into the state container (struct icc_bwmon), just store
a pointer to it.

This simplifies a bit the code and allows later to grow easily the
variant-specific data for new BWMON v5.

Cc: Rajendra Nayak <quic_rjendra@quicinc.com>
Cc: Sibi Sankar <quic_sibis@quicinc.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Sibi Sankar <quic_sibis@quicinc.com>
Tested-by: Steev Klimaszewski <steev@kali.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220728113748.170548-5-krzysztof.kozlowski@linaro.org