qom: Make enum string tables const-correct

The enum string table parameters in various QOM/QAPI methods
are declared 'const char *strings[]'. This results in const
warnings if passed a variable that was declared as

   static const char * const strings[] = { .... };

Add the extra const annotation to the parameters, since
neither the string elements, nor the array itself should
ever be modified.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c
index a14a1c7..d7f92c5 100644
--- a/qapi/qapi-dealloc-visitor.c
+++ b/qapi/qapi-dealloc-visitor.c
@@ -156,7 +156,8 @@
 {
 }
 
-static void qapi_dealloc_type_enum(Visitor *v, int *obj, const char *strings[],
+static void qapi_dealloc_type_enum(Visitor *v, int *obj,
+                                   const char * const strings[],
                                    const char *kind, const char *name,
                                    Error **errp)
 {