genksyms: reduce type_qualifier directly to decl_specifier

A type_qualifier (const, volatile, etc.) is not a type_specifier.

According to K&R [1], a type-qualifier should be directly reduced to
a declaration-specifier.

<declaration-specifier> ::= <storage-class-specifier>
| <type-specifier>
| <type-qualifier>

[1]: https://cs.wmich.edu/~gupta/teaching/cs4850/sumII06/The%20syntax%20of%20C%20in%20Backus-Naur%20form.htm

Signed-off-by: Masahiro Yamada <[e-mail]>
Acked-by: Nicolas Schier <[e-mail]>

scripts/genksyms/parse.y

···
 		  $$ = $1;
 		}
 	| type_specifier
+	| type_qualifier
 	;
 
 storage_class_specifier:
···
 
 type_specifier:
 	simple_type_specifier
-	| type_qualifier
 	| TYPEOF_KEYW '(' parameter_declaration ')'
 	| TYPEOF_PHRASE