FROMLIST: clk: fix inconsistent use of req_rate

FROMLIST: clk: fix inconsistent use of req_rate

The req_rate property seems to be made to hold the rate requested through
clk_set_rate. Currently it gets initialized in clk_init to the clocks
current rate and then adapted in clk_set_rate calls. Orphan clocks and
their children get initialized to a rate of 0 and req_rate never gets
re-set when these lose their orphan-status.

Initializing req_rate to the clocks rate also is unintuitive as it just
copies the value that is already in the rate property and also looses the
information if a component actually requested a specific rate.

So separate the requested rate and only set it in clk_core_set_rate_nolock
when a real rate gets requested. The users of the req_rate __clk_put and
clk_set_rate_range that adjust a clock based on that value use req_rate
at first and fall back to rate if no rate had been requested now.

(am from https://patchwork.kernel.org/patch/8993751/)

Change-Id: I9e345e1e9d0c101d5c3c7064b6c2d2724f9eac4f
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>