multiboot2: framebuffer: fix wrong display fmt

multiboot2/src/framebuffer.rs

@@ -93,7 +93,7 @@ pub struct FramebufferColor {
 
 /// Error when an unknown [`FramebufferTypeId`] is found.
 #[derive(Debug, Copy, Clone, Display, PartialEq, Eq)]
-#[display(fmt = "Unknown framebuffer type _0")]
+#[display(fmt = "Unknown framebuffer type {}", _0)]
 pub struct UnknownFramebufferType(u8);
 
 #[cfg(feature = "unstable")]