After switching to HR timers for RS485 the NULL checks for the object
inside timer functions become useless.

Remove them to avoid confusion to static analyzers.

Fixes 6e0a5de2 ("serial: 8250: Use hrtimers for rs485 delays")
Cc: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>