Fix qemu command to not warn about raw disk image file

Rsconscript

@@ -34,5 +34,5 @@ uefi_env = env "uefi" do |env|
 end
 
 task "run" do
-	sh %W[qemu-system-x86_64 -bios OVMF.fd -hda #{uefi_env.expand("^/efi-loader.img")}]
+	sh %W[qemu-system-x86_64 -bios OVMF.fd -drive file=#{uefi_env.expand("^/efi-loader.img")},format=raw]
 end