clk: tegra: periph: Fix error handling and resolve unsigned compare warning

./drivers/clk/tegra/clk-periph.c:59:5-9: WARNING:
	Unsigned expression compared with zero: rate < 0

The unsigned long 'rate' variable caused:
- Incorrect handling of negative errors
- Compile warning: "Unsigned expression compared with zero"

Fix by changing to long type and adding req->rate cast.

Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
Link: https://lore.kernel.org/r/79c7f01e29876c612e90d6d0157fb1572ca8b3fb.1752046270.git.xiaopei01@kylinos.cn
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/tegra/clk-periph.c

@@ -51,7 +51,7 @@ static int clk_periph_determine_rate(struct clk_hw *hw,
 	struct tegra_clk_periph *periph = to_clk_periph(hw);
 	const struct clk_ops *div_ops = periph->div_ops;
 	struct clk_hw *div_hw = &periph->divider.hw;
-	unsigned long rate;
+	long rate;
 
 	__clk_hw_set_clk(div_hw, hw);
 
@@ -59,7 +59,7 @@ static int clk_periph_determine_rate(struct clk_hw *hw,
 	if (rate < 0)
 		return rate;
 
-	req->rate = rate;
+	req->rate = (unsigned long)rate;
 	return 0;
 }