Ensure fields of SyncRect are not reordered

Without repr(C), repr(packed) technically allows reordering fields.

graphics/fbcond/src/display.rs

@@ -13,7 +13,7 @@ use syscall::{O_CLOEXEC, O_NONBLOCK, O_RDWR};
 
 // Keep synced with vesad
 #[derive(Clone, Copy)]
-#[repr(packed)]
+#[repr(C, packed)]
 pub struct SyncRect {
     pub x: i32,
     pub y: i32,

graphics/vesad/src/screen.rs

@@ -9,7 +9,7 @@ use crate::display::OffscreenBuffer;
 
 // Keep synced with orbital
 #[derive(Clone, Copy)]
-#[repr(packed)]
+#[repr(C, packed)]
 pub struct SyncRect {
     pub x: i32,
     pub y: i32,