linux

If clk_round_rate(clk, ULONG_MAX) is called to acquire the highest
available clock rate and the highest available clock rate is smaller
than ULONG_MAX/2, the result of "req->rate - tmp_req.rate" has the
highest bit set. Since the input to abs() is signed, that means the
number will be miss-interpreted.

This results in the logic being reverted and the worst choice being
selected as the best one. For example this has been observed on RK3588
for the eMMC clock:

GPLL:   abs(18446744073709551615 - 1188000000) = 1188000001
CPLL:   abs(18446744073709551615 - 1500000000) = 1500000001
XIN24M: abs(18446744073709551615 -   24000000) =   24000001

With the updated logic any casting between signed and unsigned is
avoided and the numbers look like this instead:

GPLL:   18446744073709551615 - 1188000000 = 18446744072521551615
CPLL:   18446744073709551615 - 1500000000 = 18446744072209551615
XIN24M: 18446744073709551615 -   24000000 = 18446744073685551615

As a result the parent with the highest acceptable rate is chosen
instead of the parent clock with the lowest one.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>