kconfig: fix possible buffer overflow

Buffer 'new_argv' is accessed without bound check after accessing with
bound check via 'new_argc' index.

Fixes: e298f3b4 ("kconfig: add built-in function support")
Co-developed-by: Ivanov Mikhail <ivanov.mikhail1@huawei-partners.com>
Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/preprocess.c

@@ -396,6 +396,9 @@ static char *eval_clause(const char *str, size_t len, int argc, char *argv[])
 
 		p++;
 	}
+
+	if (new_argc >= FUNCTION_MAX_ARGS)
+		pperror("too many function arguments");
 	new_argv[new_argc++] = prev;
 
 	/*