serial: core: drop redundant sysrq checks

The sysrq timestamp will never be set unless port->has_sysrq is set (see
uart_handle_break()) so drop the redundant checks that were added by
commit 1997e9df

 ("serial_core: Un-ifdef sysrq SUPPORT_SYSRQ").

Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Link: https://lore.kernel.org/r/20200610152232.16925-4-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>