net: ipa: use struct_size() for the interconnect array

In review for commit 8ee7ec48 ("net: ipa: embed interconnect
array in the power structure"), Jakub Kicinski suggested that a
follow-up patch use struct_size() when computing the size of the
IPA power structure, which ends with a flexible array member.

Do that.
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20220311162423.872645-1-elder@linaro.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ipa/ipa_power.c

@@ -374,8 +374,8 @@ ipa_power_init(struct device *dev, const struct ipa_power_data *data)
 		goto err_clk_put;
 	}
 
-	size = data->interconnect_count * sizeof(power->interconnect[0]);
-	power = kzalloc(sizeof(*power) + size, GFP_KERNEL);
+	size = struct_size(power, interconnect, data->interconnect_count);
+	power = kzalloc(size, GFP_KERNEL);
 	if (!power) {
 		ret = -ENOMEM;
 		goto err_clk_put;