kconfig: fix memory leak from range properties

Currently, sym_validate_range() duplicates the range string using
xstrdup(), which is overwritten by a subsequent sym_calc_value() call.
It results in a memory leak.

Instead, only the pointer should be copied.

Below is a test case, with a summary from Valgrind.

[Test Kconfig]

  config FOO
          int "foo"
          range 10 20

[Test .config]

  CONFIG_FOO=0

[Before]

  LEAK SUMMARY:
     definitely lost: 3 bytes in 1 blocks
     indirectly lost: 0 bytes in 0 blocks
       possibly lost: 0 bytes in 0 blocks
     still reachable: 17,465 bytes in 21 blocks
          suppressed: 0 bytes in 0 blocks

[After]

  LEAK SUMMARY:
     definitely lost: 0 bytes in 0 blocks
     indirectly lost: 0 bytes in 0 blocks
       possibly lost: 0 bytes in 0 blocks
     still reachable: 17,462 bytes in 20 blocks
          suppressed: 0 bytes in 0 blocks
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/symbol.c

@@ -122,9 +122,9 @@ static long long sym_get_range_val(struct symbol *sym, int base)
 static void sym_validate_range(struct symbol *sym)
 {
 	struct property *prop;
+	struct symbol *range_sym;
 	int base;
 	long long val, val2;
-	char str[64];
 
 	switch (sym->type) {
 	case S_INT:
@@ -140,17 +140,15 @@ static void sym_validate_range(struct symbol *sym)
 	if (!prop)
 		return;
 	val = strtoll(sym->curr.val, NULL, base);
-	val2 = sym_get_range_val(prop->expr->left.sym, base);
+	range_sym = prop->expr->left.sym;
+	val2 = sym_get_range_val(range_sym, base);
 	if (val >= val2) {
-		val2 = sym_get_range_val(prop->expr->right.sym, base);
+		range_sym = prop->expr->right.sym;
+		val2 = sym_get_range_val(range_sym, base);
 		if (val <= val2)
 			return;
 	}
-	if (sym->type == S_INT)
-		sprintf(str, "%lld", val2);
-	else
-		sprintf(str, "0x%llx", val2);
-	sym->curr.val = xstrdup(str);
+	sym->curr.val = range_sym->curr.val;
 }
 
 static void sym_set_changed(struct symbol *sym)