platform: msm: msm_bus: Correct the QoS clk node parsing

Correct the QoS clk node parsing to use of_get_child_node_by_name()
instead of_find_node_by_name() property other wise we'd end up with
incorrect device_nodes and perform illegal system operations.

Change-Id: I8082d3420a911b1c9a23376617fb000828b19fd8
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>