clk: qcom: Fix incorrect mux_get_parent mapping

The current mux_get_parent logic attempts to find the parent index by
passing the HW parent to qcom_find_src_index, which compares against the
logical value (parent_map::src) instead of the raw HW value
(parent_map::cfg). This can lead to improperly parented muxes or orphans
since there is no guarantee that the logical values match the HW values.

Add a new helper function (qcom_find_cfg_index), which returns the index
associated with the HW parent value (parent_map::cfg). Call this
function in mux_get_parent instead of qcom_find_src_index to fix the
improper mux parents.

Change-Id: I87efb8a798ab481a86d29a9b830cbc1f889a4e5b
Signed-off-by: Mike Tipton <mdtipton@codeaurora.org>