pwm: cros-ec: Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the new TRAILING_OVERLAP() helper to fix the following warnings:

drivers/pwm/pwm-cros-ec.c:53:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/pwm/pwm-cros-ec.c:87:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM)
and a set of members that would otherwise follow it. This overlays
the trailing members onto the FAM while preserving the original
memory layout.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/aJtRPZpc-Lv-C6zD@kspp
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: GustavoARSilva

drivers/pwm/pwm-cros-ec.c

@@ -49,10 +49,9 @@ static int cros_ec_pwm_set_duty(struct cros_ec_pwm_device *ec_pwm, u8 index,
 				u16 duty)
 {
 	struct cros_ec_device *ec = ec_pwm->ec;
-	struct {
-		struct cros_ec_command msg;
+	TRAILING_OVERLAP(struct cros_ec_command, msg, data,
 		struct ec_params_pwm_set_duty params;
-	} __packed buf;
+	) __packed buf;
 	struct ec_params_pwm_set_duty *params = &buf.params;
 	struct cros_ec_command *msg = &buf.msg;
 	int ret;
@@ -83,13 +82,12 @@ static int cros_ec_pwm_set_duty(struct cros_ec_pwm_device *ec_pwm, u8 index,
 
 static int cros_ec_pwm_get_duty(struct cros_ec_device *ec, bool use_pwm_type, u8 index)
 {
-	struct {
-		struct cros_ec_command msg;
+	TRAILING_OVERLAP(struct cros_ec_command, msg, data,
 		union {
 			struct ec_params_pwm_get_duty params;
 			struct ec_response_pwm_get_duty resp;
 		};
-	} __packed buf;
+	) __packed buf;
 	struct ec_params_pwm_get_duty *params = &buf.params;
 	struct ec_response_pwm_get_duty *resp = &buf.resp;
 	struct cros_ec_command *msg = &buf.msg;