um: Fix len of file in create_pid_file

sizeof gives us the size of the pointer variable, not of the
area it points to. So the number of bytes copied by umid_file_name()
is 8.
We should pass in the correct length of the file buffer.
Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/umid.c

@@ -220,11 +220,12 @@ static void __init create_pid_file(void)
 	char pid[sizeof("nnnnn\0")], *file;
 	int fd, n;
 
-	file = malloc(strlen(uml_dir) + UMID_LEN + sizeof("/pid\0"));
+	n = strlen(uml_dir) + UMID_LEN + sizeof("/pid\0");
+	file = malloc(n);
 	if (!file)
 		return;
 
-	if (umid_file_name("pid", file, sizeof(file)))
+	if (umid_file_name("pid", file, n))
 		goto out;
 
 	fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);