clk: samsung: fix getting Exynos4 fin_pll rate from external clocks

clk: samsung: fix getting Exynos4 fin_pll rate from external clocks

Commit 0dc83ad8bfc9 ("clk: samsung: Don't register clkdev lookup for the
fixed rate clocks") claimed registering clkdev lookup is not necessary
anymore, but that was not entirely true: Exynos4210/4212/4412 clock code
still relied on it to get the clock rate of xxti or xusbxti external
clocks.

Drop that requirement by accessing already registered clk_hw when
looking up the xxti/xusbxti rate.

Reported-by: Artur Weber <aweber.kernel@gmail.com>
Closes: https://lore.kernel.org/all/6227c1fb-d769-462a-b79b-abcc15d3db8e@gmail.com/
Fixes: 0dc83ad8bfc9 ("clk: samsung: Don't register clkdev lookup for the fixed rate clocks")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240722063309.60054-1-krzysztof.kozlowski@linaro.org
Tested-by: Artur Weber <aweber.kernel@gmail.com> # Exynos4212
Signed-off-by: Stephen Boyd <sboyd@kernel.org>