tty/serial: digicolor: remove sysrq reference

The Digicolor USART hardware does not support detecting the BREAK condition.
This means that we can't support sysrq on this hardware. Remove all reference
to sysrq from the code.

This also fixes build when sysrq is disabled:

drivers/tty/serial/digicolor-usart.c: In function 'digicolor_uart_console_write':
drivers/tty/serial/digicolor-usart.c:407:33: error: 'struct uart_port' has no member named 'sysrq'

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>