sensor: icm45686: Use explicit VLA for fifo encoded data

The size of icm45686_encoded_data fifo_payload is guaranteed
to span the full number of frames read as it was allocated during
icm45686_event_handler() buf_len_required size.

This update suppresses the static analysis warning of
out of bounds memory access at index 1 by explicitly declaring
fifo_payload to be a VLA at the end of icm45686_encoded_data.

Signed-off-by: Anthony Williams <anthony289478@gmail.com>

Author: anthony289478

drivers/sensor/tdk/icm45686/icm45686.h

@@ -82,7 +82,7 @@ struct icm45686_encoded_data {
 	struct icm45686_encoded_header header;
 	union {
 		struct icm45686_encoded_payload payload;
-		struct icm45686_encoded_fifo_payload fifo_payload;
+		FLEXIBLE_ARRAY_DECLARE(struct icm45686_encoded_fifo_payload, fifo_payload);
 	};
 };
 

drivers/sensor/tdk/icm45686/icm45686_decoder.c

@@ -476,7 +476,7 @@ static int icm45686_fifo_decode(const uint8_t *buffer,
 				void *data_out)
 {
 	struct icm45686_encoded_data *edata = (struct icm45686_encoded_data *)buffer;
-	struct icm45686_encoded_fifo_payload *frame_begin = &edata->fifo_payload;
+	struct icm45686_encoded_fifo_payload *frame_begin = edata->fifo_payload;
 	int count = 0;
 	int err;