clk: ti: dra7-atl-clock: fix a memory leak

of_clk_add_provider makes an internal copy of the parent_names property
while its called, thus it is no longer needed after this call and can
be freed.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>