gendwarfksyms: use preferred form of sizeof for allocation

The preferred form is to use the variable being allocated to, rather
than explicitly supplying a type name which might become stale.

Also do this for memset.

Suggested-by: Masahiro Yamada <[e-mail]>
Signed-off-by: Giuliano Procida <[e-mail]>
Reviewed-by: Sami Tolvanen <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

scripts/gendwarfksyms/cache.c

···
 {
 	struct cache_item *ci;
 
-	ci = xmalloc(sizeof(struct cache_item));
+	ci = xmalloc(sizeof(*ci));
 	ci->key = key;
 	ci->value = value;
 	hash_add(cache->cache, &ci->hash, hash_32(key));

scripts/gendwarfksyms/die.c

···
 {
 	struct die *cd;
 
-	cd = xmalloc(sizeof(struct die));
+	cd = xmalloc(sizeof(*cd));
 	init_die(cd);
 	cd->addr = (uintptr_t)die->addr;
 
···
 {
 	struct die_fragment *df;
 
-	df = xmalloc(sizeof(struct die_fragment));
+	df = xmalloc(sizeof(*df));
 	df->type = FRAGMENT_EMPTY;
 	list_add_tail(&df->list, &cd->fragments);
 	return df;

scripts/gendwarfksyms/dwarf.c

···
 	 * Note that the user of this feature is responsible for ensuring
 	 * that the structure actually remains ABI compatible.
 	 */
-	memset(&state.kabi, 0, sizeof(struct kabi_state));
+	memset(&state.kabi, 0, sizeof(state.kabi));
 
 	res = checkp(process_die_container(&state, NULL, die,
 					   check_union_member_kabi_status,

scripts/gendwarfksyms/kabi.c

···
 		if (type == KABI_RULE_TYPE_UNKNOWN)
 			error("unsupported kABI rule type: '%s'", field);
 
-		rule = xmalloc(sizeof(struct rule));
+		rule = xmalloc(sizeof(*rule));
 
 		rule->type = type;
 		rule->target = xstrdup(get_rule_field(&rule_str, &left));

scripts/gendwarfksyms/symbols.c

···
 			continue;
 		}
 
-		sym = xcalloc(1, sizeof(struct symbol));
+		sym = xcalloc(1, sizeof(*sym));
 		sym->name = name;
 		sym->addr.section = SHN_UNDEF;
 		sym->state = SYMBOL_UNPROCESSED;

scripts/gendwarfksyms/types.c

···
 	if (!s)
 		return 0;
 
-	entry = xmalloc(sizeof(struct type_list_entry));
+	entry = xmalloc(sizeof(*entry));
 	entry->str = s;
 	entry->owned = owned;
 	list_add_tail(&entry->list, list);
···
 	struct type_expansion *e;
 
 	if (__type_map_get(name, &e)) {
-		e = xmalloc(sizeof(struct type_expansion));
+		e = xmalloc(sizeof(*e));
 		type_expansion_init(e);
 		e->name = xstrdup(name);