clk: ti: dra7xx: fix RNG clock parent

RNG is sourced from L4 clock. Add info for this for proper parenting of
the clock.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Link: https://lkml.kernel.org/r/20200430083640.8621-4-t-kristo@ti.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>