kconfig: Make expr_copy() take a const argument

Fixes
scripts/kconfig/expr.c: In function ‘expr_get_leftmost_symbol’:
scripts/kconfig/expr.c:1026:2: warning: passing argument 1 of ‘expr_copy’ discards qualifiers from pointer target type
scripts/kconfig/expr.c:67:14: note: expected ‘struct expr *’ but argument is of type ‘const struct expr *’

Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/expr.c

@@ -64,7 +64,7 @@ struct expr *expr_alloc_or(struct expr *e1, struct expr *e2)
 	return e2 ? expr_alloc_two(E_OR, e1, e2) : e1;
 }
 
-struct expr *expr_copy(struct expr *org)
+struct expr *expr_copy(const struct expr *org)
 {
 	struct expr *e;
 

scripts/kconfig/expr.h

@@ -191,7 +191,7 @@ struct expr *expr_alloc_two(enum expr_type type, struct expr *e1, struct expr *e
 struct expr *expr_alloc_comp(enum expr_type type, struct symbol *s1, struct symbol *s2);
 struct expr *expr_alloc_and(struct expr *e1, struct expr *e2);
 struct expr *expr_alloc_or(struct expr *e1, struct expr *e2);
-struct expr *expr_copy(struct expr *org);
+struct expr *expr_copy(const struct expr *org);
 void expr_free(struct expr *e);
 int expr_eq(struct expr *e1, struct expr *e2);
 void expr_eliminate_eq(struct expr **ep1, struct expr **ep2);