sys: treat epic_stat as opaque

on rust nightly, bindgen adds another brokeness to this struct that
even prevents compiling.

card10-sys/build.rs

@@ -54,6 +54,7 @@ fn main() -> Result<(), Box<dyn Error>> {
         .clang_arg("-Ifirmware/lib/sdk/Libraries/MAX32665PeriphDriver/Include")
         .header("vendor/wrapper.h")
         .ctypes_prefix("ctypes")
+        .opaque_type("epic_stat")
         .generate()
         .map_err(|_| "Couldn't generate bindings")?;