vmm: Define riscv64 UEFI Error

Error::UefiLoad is required for load_firmware to propagate errors
encountered, define it for riscv64.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

vmm/src/vm.rs

@@ -116,6 +116,10 @@ pub enum Error {
     #[error("Cannot load the UEFI binary in memory")]
     UefiLoad(#[source] arch::aarch64::uefi::Error),
 
+    #[cfg(target_arch = "riscv64")]
+    #[error("Cannot load the UEFI binary in memory")]
+    UefiLoad(#[source] arch::riscv64::uefi::Error),
+
     #[error("Cannot load the initramfs into memory")]
     InitramfsLoad,