printk: printk: Remove unnecessary statements＇len = 0;＇

In the following two functions, len has already been assigned a value of
0 when defining the variable, so remove 'len=0;'.

Signed-off-by: Li kunyu <kunyu@nfschina.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20231023062359.130633-1-kunyu@nfschina.com