acpigen: Correctly handle root scope

Change-Id: I9b3c9109b01e348259e64e93a4397212216ab152
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/6799
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/arch/x86/boot/acpigen.c

@@ -223,7 +223,12 @@ int acpigen_emit_namestring(const char *namepath) {
 		namepath++;
 	}
 
-	ASSERT(namepath[0] != '\0');
+	/* If we have only \\ or only ^...^. Then we need to put a null
+	   name (0x00). */
+	if(namepath[0] == '\0') {
+		len += acpigen_emit_byte(0x00);
+		return len;
+	}
 
 	i = 0;
 	while (namepath[i] != '\0') {