libefi: efi_type: fix unused, remove argsused

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12844

lib/libefi/rdwr_efi.c

@@ -1564,6 +1564,7 @@ efi_type(int fd)
 	}
 	return (0);
 #else
+	(void) fd;
 	return (ENOSYS);
 #endif
 }