bus: tegra-aconnect: Use of_pm_clk_add_clk()

Commit 498b5fdd

 ("PM / clk: Add support for adding a specific clock
from device-tree") add a new helper function for adding a clock from
device-tree to a device. Update the Tegra ACONNECT driver to use this
new function to simplify the driver.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>